Ad-tech glossary: 50 essential terms every developer should know
Ad-tech has the densest acronym soup in software. This glossary explains the fifty terms a developer joining the field actually encounters in their first month — in plain language, in the order an engineer needs them, not the order a marketing dictionary lists them. Alphabetized for reference, written so each entry stands alone.
A
Ad Server
The system that decides which ad to show and records the impression. First-party ad servers (publishers) and third-party ad servers (advertisers) both exist. The publisher’s ad server picks a winning campaign from many candidates; the advertiser’s ad server delivers the creative, counts impressions independently, and reconciles billing with the publisher. Discrepancies between publisher and advertiser counts above 5–10% are a normal source of monthly reconciliation work and trace to caching, late beacons, and IVT filtering differences.
ADM (Ad Markup)
The string field on a bid response (bid.adm) that contains the actual creative payload: HTML, a script tag, a VAST document, or a native JSON bundle. ADM is what gets rendered in the user’s browser or app. If you are debugging a broken creative, ADM is the first thing you inspect. When ADM is absent, the markup is fetched lazily from bid.nurl after the auction completes, which trades off a small latency penalty for the ability to defer rendering decisions to the buyer.
atbid
A field on some OpenRTB bid responses that signals the auction type used for the bid (first-price, second-price, fixed-price). Useful for downstream analytics, especially when a single DSP integrates with multiple exchanges that run different auction mechanics. The canonical OpenRTB spec defines it as at on the request and reflects auction semantics on the response. Mismatches between requested and applied auction type are a common cause of bid-shading miscalibration.
B
Bid Request
The JSON document a supply-side platform sends to demand-side platforms describing an available impression: the user (anonymized), the page or app, the ad slot, and any restrictions. Each request waits up to tmax milliseconds for a response. See our OpenRTB introduction for the full schema.
Bid Response
The JSON document a DSP returns when it wants to buy an impression. Contains one or more seatbid objects, each with one or more bid objects holding the price, creative, and tracking URLs. Empty or absent responses count as “no bid.”
Bid Floor
The minimum CPM a publisher will accept for an impression, expressed as imp.bidfloor in the bid request. Bids below the floor are dropped by the exchange before the auction. Floors are how publishers protect inventory value from getting commoditized to zero.
Brand Safety
The discipline of preventing ads from appearing next to content that damages the advertiser’s reputation — hate speech, violence, misinformation, certain news topics. Implemented via keyword filters, page classifiers, and third-party verification vendors. Increasingly distinguished from suitability, which is finer-grained and lets each advertiser define its own thresholds rather than relying on a single industry-wide block list. The GARM framework, before its 2024 dissolution, set the common vocabulary that most vendors still use.
burl
The billing notice URL on a bid response. The exchange calls it when the impression has been billed, signalling to the DSP that money will change hands. Distinct from nurl (win notice) and from impression beacons in the ADM.
C
CPC (Cost per Click)
A pricing model where the advertiser pays only when a user clicks the ad. Common in search and direct-response display. Easy to attribute, but exposes the buyer to click-fraud risk.
CPM (Cost per Mille)
Cost per thousand impressions, expressed in the response currency. The default pricing unit in programmatic. A bid of 1.42 at CPM means $1.42 per thousand impressions, or $0.00142 per impression.
CPV (Cost per View)
Cost per video view, where “view” is defined by the platform (often 30 seconds or video completion). Used in skippable in-stream video; rare in display.
Creative
The actual ad shown to the user: the image, video, HTML5 unit, or native asset bundle. Stored in the ADM. The buyer ships it; the publisher hosts it. See our debugging guide for what goes wrong.
CRID (Creative ID)
The buyer’s unique identifier for a creative, sent on bid.crid. Used for reporting, frequency capping, and creative-level blocklisting. Two impressions of the same creative share a CRID; two different sizes of the same campaign usually do not.
CTR (Click-Through Rate)
Clicks divided by impressions, expressed as a percentage. Display ads sit around 0.05–0.10% on average. Video and native run higher. Anomalously high CTRs (above 1%) often indicate invalid traffic rather than a successful campaign.
D
DSP (Demand-Side Platform)
The buyer’s platform: aggregates advertiser budgets, evaluates bid requests, decides what to bid, and tracks performance. DSPs talk to many exchanges in parallel, sometimes hundreds of thousands of bid requests per second. The engineering challenge is responding under tmax while running predictive models on every request — large DSPs run sub-100-ms inference pipelines on dedicated low-latency clusters near the exchanges they bid into.
E
eCPM (Effective CPM)
The CPM-equivalent of a non-CPM campaign. If a CPC campaign at $0.50 per click delivers a 0.2% CTR, the eCPM is $1.00 (0.002 × 1000 × $0.50). Publishers use eCPM to compare CPC, CPV, and CPM demand on the same yardstick.
Exchange
The auction venue. Receives impression requests from supply, fans them out to demand, runs the auction, returns the winner. Some exchanges are owned by SSPs; some are independent. The largest run real-time auctions for tens of millions of impressions per second. Exchanges differ in fee structure (a percentage take rate on cleared CPM), in auction type (first vs second price), and in supply-path optimization preferences, all of which materially affect what buyers see.
F
Fill Rate
The percentage of impressions for which the publisher actually delivered an ad. A 95% fill rate means 5 of every 100 ad calls returned no ad — either no bid, or every bid was below floor. Fill rate is one of the headline KPIs publishers track.
First-price auction
The winning bid pays its full bid amount. Now the dominant auction type after Google Ad Manager and most header-bidding wrappers switched in 2019. Forces buyers to bid-shade strategically.
Floor Price
Synonym for bid floor. See above.
Footer Bid
An adapter pattern where the publisher loads bid logic in the page footer rather than the header, deferring auction latency until after critical content has rendered. Trades a small drop in fill rate for faster page load.
G
GDPR / TCF
The EU General Data Protection Regulation governs how personal data is collected and processed. The IAB Transparency & Consent Framework (TCF) is the ad industry’s standardized way of passing user consent signals through the supply chain. TCF v2.2 is current; the consent string is base64-encoded and travels as user.ext.consent on bid requests.
H
Header Bidding
A technique where publishers solicit bids from multiple SSPs in parallel from the browser before calling their primary ad server. Replaces the historical “waterfall” with simultaneous auctions and typically lifts revenue 10–30%. The original implementation ran in the browser (client-side header bidding); the modern variant runs server-to-server (server-side header bidding) to reduce client weight at the cost of losing access to the user’s browser context. See our intro article.
I
IAB
Interactive Advertising Bureau. The industry trade body that maintains the specs that hold the ecosystem together: OpenRTB, VAST, VPAID, OMID, ads.txt, TCF. Most ad-tech engineering boils down to implementing IAB specs. The IAB Tech Lab is the engineering arm; the IAB itself is broader and includes policy and standards work. National chapters (IAB UK, IAB Europe) sometimes publish their own variants for local compliance, particularly around consent.
IDFA / GAID
Identifier for Advertisers (Apple) and Google Advertising ID (Android). Per-device, user-resettable identifiers used for cross-app attribution and audience targeting. iOS 14.5 made IDFA opt-in; opt-in rates sit around 25%. Android followed with a similar restriction.
Impression
One delivery of one ad to one user. The atomic unit of ad inventory. An impression fires when the ad markup is loaded; a viewable impression additionally requires that the ad be visible per IAB viewability rules. Counting is harder than it sounds: an impression beacon may fire before the creative paints (counting an unrendered ad) or never fire (an ad-blocker dropped the request). MRC-accredited measurement vendors arbitrate the differences.
IVT (Invalid Traffic)
Traffic that does not represent a genuine human user: bots, scrapers, click farms, hijacked devices. IAB splits IVT into General (GIVT — spider lists, datacenter IPs) and Sophisticated (SIVT — harder to detect). Verification vendors (HUMAN, IAS, DoubleVerify) sell IVT detection as a service.
M
Mediation
The SDK pattern, common in mobile apps, where one SDK orchestrates calls to many ad networks in sequence or in parallel. The SDK picks the network most likely to fill at the best price. Effectively, header bidding for native apps.
MRAID
Mobile Rich Media Ad Interface Definitions. The IAB’s JavaScript API for rich-media ads inside in-app WebViews. Provides mraid.getState(), mraid.open(), mraid.expand(), and similar bridges between the creative and the host app. MRAID 3.0 is the current version; MRAID 2.0 still dominates in the field. Creatives that depend on MRAID will appear to do nothing when previewed in a desktop browser — the mraid global does not exist outside a host SDK. Always stub it when debugging app creatives on the web.
N
nurl / burl
The win-notice URL and billing-notice URL on a bid response. The exchange calls nurl when the bid wins and burl when the impression bills. They are independent of impression beacons in the ADM; correct accounting requires all three to be reconciled.
O
OMID (Open Measurement)
The IAB’s framework for letting third-party verification scripts measure viewability and IVT inside any ad slot — web, in-app, or CTV — through a standardized interface (OM SDK). Eliminates the historical mess of bespoke per-vendor SDKs in each publisher app: instead of integrating with each verification vendor individually, publishers integrate OM SDK once and any OMID-compliant verification script works through the same channel.
OpenRTB
The IAB protocol that defines the JSON schemas for bid requests and bid responses. Versions 2.5 and 2.6 are both in production; 3.0 is a major redesign with cleaner separation of impression and creative objects but has slow industry uptake. The protocol is intentionally permissive — many fields are optional — which means real-world interoperability is more about implementing the dialect each exchange actually expects than about the spec on paper. See our primer.
ORTB Renderer
A debug tool that takes a raw OpenRTB bid response (or just the bid.adm) and renders the creative in an iframe so a human can see what it would look like in production. Our free version supports banner, native, and VAST inputs.
P
Prebid
The dominant open-source header-bidding library. Prebid.js for web, Prebid Mobile for native apps, Prebid Server for server-to-server bidding. Maintained by Prebid.org, a coalition of publishers, SSPs, and DSPs. Each SSP ships a bid adapter module that translates between Prebid’s internal protocol and the SSP’s native API; the adapter list in the public repo is the de facto roster of integrated demand partners.
Programmatic
Umbrella term for automated, auction-based ad buying. Distinguished from direct sales (hand-shaken contracts between buyer and seller) and from traditional ad networks. Programmatic is now ~90% of digital display by spend in most major markets. The term covers open-market RTB, private marketplaces (PMPs — invitation-only auctions), and programmatic guaranteed (fixed-price, fixed-volume deals served through programmatic pipes).
Publisher
The owner of the inventory: a website, an app, a streaming service, a podcast. Publishers monetize by selling impressions on their content. In the supply chain, publishers sit upstream of SSPs.
R
RTB (Real-Time Bidding)
The auction mechanism by which most programmatic transactions happen: every impression goes to a sub-second auction, with the highest bidder winning. OpenRTB is the protocol implementing RTB. The “real-time” part is the constraint that fundamentally shapes the engineering: every component of the chain — encoding, network hop, bidder evaluation, response decoding — must complete within a hundred milliseconds or so or the impression is lost.
RTBcrid
The CRID field as it appears in an RTB bid response (bid.crid). Also the namesake of this site — a creative-debugging toolkit built around inspecting the contents of adm for a given CRID.
S
Mobile SDK
Software Development Kit. In ad-tech context, the in-app library that lets a publisher monetize through a specific network. Mobile SDKs are notoriously heavy — a typical mediation stack with five networks adds 2–5 MB to the binary, and each SDK runs background threads that contend for CPU, memory, and network. SDK consolidation is an ongoing trend, with mediation platforms offering single-binary alternatives to multi-SDK stacks.
Second-price auction
The winning bid pays one cent more than the runner-up. Historically dominant in RTB because it incentivizes truthful bidding (Vickrey-style), but largely replaced by first-price after concerns about transparency and tiered auctions.
Seat
An identifier for a buyer within an exchange — conceptually like a trading desk seat on an exchange. One DSP may have many seats representing different advertiser accounts. The bid.seat field carries it on the response.
Site / App
OpenRTB requests carry exactly one of site (for web inventory) or app (for in-app inventory). Each object holds the publisher’s domain or bundle, IAB content categories, and a publisher reference. Buyers gate targeting on these fields.
SSP (Supply-Side Platform)
The publisher’s platform: aggregates publisher inventory, runs the auction with multiple buyers, and manages floor prices and demand sources. The mirror image of a DSP. Modern SSPs handle yield optimization, supply-path optimization signals, and consent management on behalf of the publisher, in addition to running the auction itself.
T
tmax
The maximum time, in milliseconds, that the exchange will wait for bid responses. A typical tmax is 80–300 ms. Bidders that exceed it are timed out and dropped from the auction, regardless of their bid price.
TCF (Transparency & Consent Framework)
The IAB’s machine-readable consent format for GDPR compliance. The consent string encodes which vendors and purposes the user agreed to. Bidders must check the string before processing personal data.
V
VAST
Video Ad Serving Template. The IAB XML spec for video ads: defines media files, tracking events, click-throughs, companion banners, and ad pods. VAST 4.2 is current. See our deep dive.
VPAID
Video Player-Ad Interface Definition. An older JavaScript-based interactive video format. Powerful but heavy and a frequent source of viewability and IVT issues. Largely deprecated in favor of VAST 4 + OMID, though legacy VPAID inventory still exists.
Viewability
Whether an ad was actually seen. IAB’s baseline definition: at least 50% of the ad in the viewport for at least one continuous second (display) or two seconds with video playing (video). MRC-accredited measurement is the standard. Most direct buys now guarantee a minimum viewable rate, often 70–80% for display and higher for video. Below-the-fold inventory, mobile interstitials, and CTV present different measurement challenges with their own format-specific rules.
W
Waterfall
The historical, sequential demand pattern: try network A, if unfilled try network B, then C, then D. Inefficient because high-CPM demand at network C never sees the impression if network A fills with a lower-paying ad. Header bidding replaced waterfalls for most publishers; mediation waterfalls still exist in older mobile apps, and even modern mediation often falls back to waterfall behaviour for networks that do not support real-time bidding.
Win Notice
The HTTP call the exchange makes to the winning DSP’s nurl when the auction resolves. Macros in the nurl (like ${AUCTION_PRICE}) are expanded with the clearing price so the DSP can record what it actually paid. Distinct from the billing notice (burl) and the impression beacon.
Y
Yield Management
The publisher-side discipline of maximizing revenue per impression: setting floors, picking demand partners, balancing direct and programmatic, tuning ad density and viewability. A yield manager’s job is to extract every dollar from the inventory without driving users away. Sophisticated yield ops teams run their own A/B tests on floor levels, ad-stack ordering, refresh intervals, and timeout values, treating monetization as a continuously tuned system rather than a static configuration.