Digital advertising glossary

One-sentence definitions, grouped alphabetically. Where a term has a formula, it is included; the metrics page explains how to read them together.

Published by AdFire Digital · Updated July 26, 2026 · Educational guide, independently written

Advertising concepts connected around a central campaign system — Advertising terms form a system: inventory, audiences, auctions, measurement and business outcomes affect one another.

Start with four families of terms

The fastest way to learn the vocabulary is to attach each term to the question it answers. Buying terms explain how an impression becomes available and how an advertiser competes for it. Delivery terms describe whether the ad appeared and had an opportunity to be seen. Response terms describe what people did after exposure. Business terms connect that response to cost, revenue or customer value.

Family	Core question	Examples	Decision it supports
Buying	How was media purchased?	DSP, SSP, exchange, RTB, bid	Choose a channel or supply path
Delivery	Did the ad render for an eligible opportunity?	Impression, reach, frequency, viewability	Control exposure and inventory quality
Response	What did the audience do?	Click, CTR, landing-page view, conversion rate	Diagnose creative and destination performance
Business outcome	Was the response economically useful?	CPA, ROAS, CAC, LTV	Allocate budget against value

Follow the buying and delivery chain

On search and social platforms, the buying interface, auction and inventory live inside one walled garden. On the open internet, an advertiser may use a DSP while a publisher uses an SSP, with an exchange connecting their bid messages. Programmatic and RTB are related but not interchangeable: programmatic describes automated media buying broadly, while RTB describes per-impression auctions within that larger system. Private marketplace and guaranteed transactions can also be programmatic without using an open auction.

An impression records delivery under a system's counting rules; it does not prove that a human paid attention. Viewability adds an opportunity-to-see standard. Invalid-traffic filtering asks whether delivery appears legitimate. Reach estimates unique people, while frequency divides impressions by reach to estimate repeated exposure. These terms answer different questions and should not be merged into a vague “visibility” metric.

Read performance metrics as a connected system

CPM prices delivery, CTR expresses clicks as a share of impressions, CPC prices clicks and conversion rate expresses outcomes as a share of visits or clicks. Those values connect mathematically. A lower CPC may come from a lower CPM, a higher CTR or both. A lower CPA can come from a lower CPC, a higher conversion rate or a different mix of conversions. The metrics guide provides the formulas and a complete worked example.

ROAS uses revenue, not profit. CAC usually refers to the cost of acquiring a customer, which can include more than media spend. LTV estimates value over a customer relationship and depends on retention, margin and the time horizon. When reports use these terms, inspect the numerator, denominator and attribution window before comparing them.

Use terms to troubleshoot a campaign

If delivery is low, inspect eligibility, bid, budget, audience size and available inventory.
If delivery is healthy but response is weak, inspect the audience-to-creative relationship, placement and message.
If clicks arrive but conversions do not, verify tracking, landing-page relevance, speed, offer and form or checkout behavior.
If conversions arrive but economics fail, compare CPA or CAC with margin-adjusted value rather than chasing CTR.
If platform and analytics totals disagree, document the attribution model, conversion window, timezone and modeled outcomes before declaring either system wrong.

This sequence prevents a common category error: solving a landing-page problem with a higher bid, or solving an inventory-quality problem with new creative. The vocabulary is useful when each term points to a specific layer of the system. Put those layers into a written measurement plan before launch.

Alphabetical definitions

Ad exchange: A digital marketplace where publishers offer ad impressions and advertisers buy them through automated auctions.
Ad group: A container inside a campaign holding a tightly themed set of keywords or audiences plus the ads shown to them.
Ad rank: The score a search platform uses to order ads, combining the bid with expected ad quality and relevance.
ads.txt: A public text file where publishers declare which companies are authorised to sell their ad inventory, used to fight counterfeit impressions.
Attribution: The rules used to credit a conversion to one or more ad interactions — last-click, first-click, data-driven and so on.
Behavioural targeting: Selecting audiences by observed online behaviour — pages visited, content consumed, products viewed — rather than by demographics.
Bid: The maximum price an advertiser offers for a click, impression or conversion in an ad auction.
Brand safety: Controls and verification that keep ads from appearing next to content the advertiser considers unsuitable.
Broad match: The loosest keyword match type, showing ads for searches the platform judges related to the keyword's meaning.
Contextual targeting: Placing ads based on the content of the page being viewed rather than on who is viewing it.
Conversion: The defined action a campaign optimises for — a purchase, lead, signup or app install.
Conversion rate: conversions ÷ clicks — the share of ad-driven visits that complete the desired action.
Cookie: A small browser file historically used to recognise users across sites for targeting and measurement; being phased out in major browsers.
CPA (cost per action): spend ÷ conversions — the average cost of one conversion.
CPC (cost per click): spend ÷ clicks — the average price paid per click.
CPM (cost per mille): spend ÷ impressions × 1000 — the price of one thousand ad impressions.
CTR (click-through rate): clicks ÷ impressions — the share of impressions that produced a click.
Custom audience: An audience built from the advertiser's own data, such as customer lists or site visitors tagged by a pixel.
Dayparting: Scheduling ads or adjusting bids by time of day or day of week.
DSP (demand-side platform): Software advertisers use to buy impressions across many publishers and exchanges automatically.
Dynamic creative: Ads assembled on the fly from components — images, headlines, offers — chosen per impression by the platform.
First-party data: Information a company collects directly from its own customers and visitors, with consent.
Frequency: impressions ÷ unique users — average number of times one person sees an ad.
Frequency cap: A limit set on how often the same user may be shown an ad within a period.
Geo-targeting: Restricting ad delivery to chosen countries, regions, cities or radii around a point.
Impression: One served instance of an ad, whether or not it was noticed.
Invalid traffic (IVT): Impressions or clicks generated by bots or fraud rather than genuine users.
Keyword: A term an advertiser bids on in search advertising, matched against user queries by match-type rules.
Landing page: The page a user reaches after clicking an ad; its relevance and speed strongly affect conversion rate and ad quality scores.
Lookalike audience: New users a platform selects because they statistically resemble an advertiser's existing customers.
LTV (lifetime value): The total net revenue expected from a customer over the whole relationship.
Native advertising: Ads designed to match the look and format of the surrounding editorial content, labelled as advertising.
Negative keyword: A term that blocks an ad from showing, used to filter out irrelevant searches.
Pixel (tag): A snippet placed on a website that reports visits and conversions back to an ad platform.
PMP (private marketplace): An invitation-only programmatic auction where selected buyers bid on a publisher's inventory.
Programmatic: The automated buying and selling of ad inventory through software and auctions rather than manual orders.
Quality score: A search platform's diagnostic rating of keyword, ad and landing-page relevance; higher quality lowers costs.
Reach: The number of unique people exposed to an ad at least once.
Remarketing / retargeting: Showing ads to people who previously visited your site or used your app.
ROAS (return on ad spend): revenue ÷ ad spend — revenue generated per unit of advertising cost.
RTB (real-time bidding): Per-impression auctions executed in the milliseconds while a page or app loads.
Second-price auction: An auction where the winner pays just above the runner-up's bid rather than their own maximum.
SSP (supply-side platform): Software publishers use to offer their inventory to many buyers and maximise yield.
vCPM: spend ÷ viewable impressions × 1000 — cost per thousand viewable impressions.
Viewability: The share of impressions that met the standard for being on screen — for display, at least 50% of pixels for one continuous second (two for video).
View-through conversion: A conversion credited to a user who saw an ad without clicking and later converted.
Walled garden: A platform — typically a search or social network — whose ad inventory, data and measurement are available only inside its own tools.

Reference standards

Google Ads glossary — search-ad and platform measurement terminology.
IAB Tech Lab: OpenRTB — programmatic bid-request and response terminology.
IAB Tech Lab: ads.txt — authorized seller terminology.
Media Rating Council: viewability guidelines — viewable impression definitions.