Ad Tech Glossary
Last updated: February 2025
A comprehensive reference of advertising technology terms used across AdTechToolkit's tools, guides, and documentation. Each definition is written for practitioners — concise enough for a quick refresher yet detailed enough to be useful when you need context. Terms are organized into six categories covering the major domains of ad tech infrastructure.
Video Advertising
VAST
Video Ad Serving Template — an IAB XML specification that describes how video ad tags, creatives, tracking pixels, and companion ads should be structured and served. VAST is the foundational standard for video ad delivery across the programmatic ecosystem.
VMAP
Video Multiple Ad Playlist — an IAB specification that defines when ad breaks should occur during video content playback. VMAP wraps VAST responses and schedules them at pre-roll, mid-roll, and post-roll positions.
VPAID
Video Player-Ad Interface Definition — an older IAB standard that allows interactive communication between a video player and an ad unit. VPAID ads can execute JavaScript, which enables rich interactivity but raises security and performance concerns.
SIMID
Secure Interactive Media Interface Definition — the IAB successor to VPAID that provides interactive ad capabilities within a sandboxed iframe. SIMID improves security and reliability compared to VPAID by isolating ad code from the player environment.
Wrapper
A VAST tag type that does not contain the final ad creative itself. Instead, a Wrapper includes a VASTAdTagURI that points to another VAST tag, forming a chain of redirects. Wrappers are used for measurement, mediation, and demand-partner chaining.
VASTAdTagURI
The XML element inside a VAST Wrapper that contains the URL pointing to the next VAST tag in the chain. Each Wrapper must include exactly one VASTAdTagURI to enable the ad player to follow the chain to the final InLine response.
InLine
A VAST tag type that contains the actual ad creative — media files, tracking URLs, companion ads, and metadata. An InLine element is the terminal node in a VAST wrapper chain and provides everything the player needs to render the ad.
MediaFile
A VAST element that specifies a video creative file, including its URL, MIME type, bitrate, dimensions, and delivery method. A single InLine ad may include multiple MediaFile elements at different quality levels for adaptive playback.
Impression
A tracking event fired when a video ad begins playing. The Impression element in VAST contains one or more pixel URLs that the player requests to signal that the ad was served and viewed. Accurate impression tracking is critical for billing and reporting.
Ad Pod
A sequence of multiple video ads served back-to-back within a single ad break, similar to a commercial break on television. Ad pods are defined in VAST 3.0 and later using the sequence attribute on Ad elements.
Pre-roll
A video ad that plays before the main content begins. Pre-roll is the most common ad placement in online video and typically has the highest viewability and completion rates among video ad positions.
Mid-roll
A video ad that plays during a break in the main content, similar to a traditional commercial break. Mid-roll ads are commonly scheduled using VMAP and tend to have strong completion rates because the viewer is already engaged.
Post-roll
A video ad that plays after the main content has finished. Post-roll ads typically have lower completion rates than pre-roll or mid-roll because viewers may navigate away once the content ends.
Companion Ad
A display banner or rich-media unit that appears alongside a video ad, typically in a designated slot on the page. Companion ads are defined within the VAST CompanionAds element and remain visible during or after video playback to reinforce the message.
IMA SDK
Interactive Media Ads SDK — Google's client-side library for requesting and rendering video ads on web, iOS, and Android. The IMA SDK handles VAST parsing, ad playback, tracking, and ad-break scheduling, and is one of the most widely adopted video ad SDKs.
SSAI
Server-Side Ad Insertion — a technique where video ads are stitched into the content stream on the server before delivery to the client. SSAI prevents ad blockers from detecting ad segments and provides a seamless viewing experience similar to broadcast television.
CSAI
Client-Side Ad Insertion — the traditional model where the video player on the viewer's device requests and renders ads separately from the content stream. CSAI offers more flexibility for interactive ad formats but is susceptible to ad blockers and can introduce buffering between content and ads.
Data Formats
JSON
JavaScript Object Notation — a lightweight, text-based data-interchange format that uses human-readable key-value pairs and arrays. JSON is the dominant format for REST API payloads, configuration files, and data exchange in web applications.
XML
Extensible Markup Language — a structured document format that uses nested tags and attributes to represent data. XML is the foundation of VAST, VMAP, and many legacy ad tech protocols, and supports schema validation via XSD.
XSD
XML Schema Definition — a W3C standard for defining the structure, elements, attributes, and data types allowed in an XML document. The IAB publishes official XSD files for each VAST version, which validators use for strict compliance checking.
CDATA
Character Data section — a block within an XML document delimited by <![CDATA[ and ]]> that tells the parser to treat the enclosed content as raw text rather than markup. CDATA sections are commonly used in VAST to embed tracking URLs that contain special characters.
Namespace
A mechanism in XML that prevents element-name collisions by associating tags with a unique URI prefix. Namespaces are used in VAST extensions and in documents that combine multiple XML vocabularies, such as VAST with custom vendor elements.
Well-formed XML
An XML document that follows all basic syntax rules: every opening tag has a matching closing tag, attributes are quoted, elements are properly nested, and there is exactly one root element. A document must be well-formed before it can be validated against an XSD schema.
Pretty Print
The process of formatting code or data with consistent indentation, line breaks, and spacing to make it easy for humans to read. Pretty printing is especially useful when inspecting minified JSON payloads or single-line VAST XML responses.
Minify
The process of removing unnecessary whitespace, line breaks, and comments from code or data to reduce file size. Minified output is compact and efficient for transmission but difficult for humans to read without re-formatting.
Encoding & Transport
Base64
A binary-to-text encoding scheme that represents arbitrary data using 64 ASCII characters (A-Z, a-z, 0-9, +, /). Base64 is widely used in ad tech to encode tokens, creative payloads, and tracking data for safe transport in text-based protocols.
Base64URL
A URL-safe variant of Base64 that replaces + with - and / with _, and typically omits trailing = padding characters. Base64URL is used when encoded data must appear in URLs or filenames without requiring additional percent-encoding.
Percent-encoding
A mechanism for encoding reserved and unsafe characters in URIs by replacing each character with a percent sign followed by two hexadecimal digits representing its byte value. Percent-encoding ensures that special characters like &, =, and spaces do not break URL structure.
Query String
The portion of a URL that follows the question mark (?) and contains key-value parameter pairs separated by ampersands (&). Query strings are used extensively in ad tech for passing targeting data, macro values, and cache-busting tokens in ad tag URLs.
URI
Uniform Resource Identifier — a string that identifies a resource by name, location, or both. URIs are defined by RFC 3986 and include both URLs (which specify how to access a resource) and URNs (which name a resource without specifying its location).
URL
Uniform Resource Locator — a specific type of URI that provides the network location and access mechanism for a resource. In ad tech, URLs are used for ad tag endpoints, tracking pixels, creative assets, and redirect destinations.
UTF-8
A variable-width character encoding that can represent every character in the Unicode standard using one to four bytes. UTF-8 is the dominant encoding for web content and is the default encoding for JSON documents and modern XML parsers.
Privacy & Consent
GDPR
General Data Protection Regulation — a European Union regulation that governs the collection, processing, and storage of personal data for individuals within the EU and EEA. GDPR requires explicit user consent before most forms of ad targeting and tracking.
TCF
Transparency and Consent Framework — an IAB Europe standard that provides a structured way for publishers, advertisers, and technology vendors to communicate user consent preferences. TCF consent strings encode which vendors and purposes the user has approved.
CMP
Consent Management Platform — a tool or service that presents consent choices to users (typically via a cookie banner or dialog), collects their preferences, and generates a TCF consent string that downstream vendors can read and respect.
Consent String
A Base64-encoded string generated by a CMP that encodes a user's consent and objection choices under the TCF specification. The consent string is passed through the ad tech supply chain so that each vendor can determine whether it has permission to process the user's data.
Global Vendor List
A centralized registry maintained by IAB Europe that lists all registered ad tech vendors participating in the TCF, along with the data-processing purposes each vendor declares. CMPs reference the GVL to present accurate vendor information to users.
Purpose Consent
A field within a TCF consent string that indicates which processing purposes the user has explicitly agreed to. Purposes include activities like storing information on a device, creating a personalized ads profile, and measuring ad performance.
Legitimate Interest
A legal basis under GDPR and the TCF that allows certain data processing without explicit consent when the vendor has a legitimate reason and the processing does not override the user's rights. Vendors must declare legitimate interest claims in the Global Vendor List.
CCPA
California Consumer Privacy Act — a US state privacy law that gives California residents the right to know what personal data is collected, to request deletion, and to opt out of the sale of their personal information. Many ad tech platforms surface a "Do Not Sell My Personal Information" link to comply with CCPA.
HTTP & Networking
HTTP Redirect
A server response that instructs the client to request a different URL. Redirects are fundamental to ad serving, where ad tags, tracking pixels, and impression URLs frequently pass through multiple intermediary servers before reaching their final destination.
301 Redirect
A permanent HTTP redirect that tells clients and search engines the resource has moved permanently to a new URL. In ad tech, 301 redirects are less common than 302s but may be used for canonical URL migrations or permanent endpoint changes.
302 Redirect
A temporary HTTP redirect that tells the client to request a different URL for this particular request. 302 redirects are the most common redirect type in ad serving, used extensively in impression tracking, click tracking, and demand-partner chaining.
Redirect Chain
A sequence of HTTP redirects that a request follows from the initial URL to the final destination. In ad tech, redirect chains can involve multiple ad servers, tracking platforms, and measurement vendors. Long chains increase latency and risk breakage if any hop fails.
User Agent
A string sent by a browser or application in the HTTP User-Agent header that describes the client software, operating system, and device type. Ad servers use the user-agent string for device targeting, creative selection, and fraud detection.
User-Agent Client Hints
A modern alternative to the traditional User-Agent string that provides device and browser information through structured HTTP headers (Sec-CH-UA, Sec-CH-UA-Platform, etc.) requested by the server. Client Hints reduce fingerprinting surface while still enabling legitimate use cases like device targeting.
Cookie
A small piece of data stored by the browser and sent with subsequent HTTP requests to the same domain. Cookies are used in ad tech for user identification, frequency capping, conversion attribution, and consent storage. Third-party cookies are being phased out by major browsers.
Set-Cookie
An HTTP response header that instructs the browser to store a cookie with specified attributes. The Set-Cookie header controls the cookie's name, value, expiration, domain, path, and security flags such as Secure, HttpOnly, and SameSite.
SameSite
A cookie attribute that controls whether a cookie is sent with cross-site requests. The three values — Strict, Lax, and None — determine the level of cross-site access. SameSite=None with the Secure flag is required for third-party cookies used in ad tech iframe and redirect flows.
HttpOnly
A cookie attribute that prevents client-side JavaScript from accessing the cookie via document.cookie. HttpOnly cookies can only be read and modified by the server, which helps protect sensitive session data from cross-site scripting (XSS) attacks.
Secure Flag
A cookie attribute that ensures the cookie is only transmitted over encrypted HTTPS connections. Setting the Secure flag prevents the cookie from being sent in plaintext over HTTP, which is essential for protecting authentication tokens and consent identifiers.
Text & Tooling
Regular Expression
A pattern-matching language used to search, match, and transform text based on defined rules. Regular expressions are invaluable in ad tech for extracting macro values from URLs, validating tag formats, and performing bulk find-and-replace operations on ad configurations.
Regex Flag
A modifier that changes how a regular expression is evaluated. Common flags include g (global — match all occurrences), i (case-insensitive), and m (multiline — treat each line as a separate string for ^ and $ anchors).
Capture Group
A portion of a regular expression enclosed in parentheses that extracts a specific substring from the matched text. Capture groups are used in find-and-replace operations to reuse matched segments in the replacement string via backreferences like $1 and $2.
HLS
HTTP Live Streaming — an adaptive-bitrate streaming protocol developed by Apple that delivers video content via an M3U8 playlist file and a series of small media segments. HLS is the dominant streaming format for video ad creatives on iOS and web platforms.
M3U8
A UTF-8 encoded playlist file used by HLS that lists the available media segments and their playback order. M3U8 files can reference multiple bitrate variants, enabling the player to switch quality levels dynamically based on network conditions.
Transport Stream
A container format (file extension .ts) used by HLS to package small segments of audio and video data. Each transport stream segment typically contains two to ten seconds of content and is referenced by the M3U8 playlist.
Directory Tree
A text-based visual representation of a folder and file hierarchy using indentation and line-drawing characters. Directory trees are commonly used in documentation, README files, and project specs to illustrate the structure of codebases, asset libraries, or configuration layouts.
Related Resources
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