Digital Advertising Glossary

The price an advertiser pays for one thousand ad impressions. 'Mille' is Latin for thousand. The dominant pricing model for brand and display advertising, where the goal is to be seen rather than necessarily clicked.

Why it matters: CPM lets you compare the cost of reach across very different placements and formats on a like-for-like basis. It's the baseline currency of programmatic display and the figure most publishers and ad networks quote first.

The amount an advertiser pays each time someone clicks their ad. The advertiser pays nothing for impressions — only for the click that sends a user to their site. The standard model for search and performance campaigns.

Why it matters: CPC ties cost directly to a concrete action, shifting the risk of a poorly-performing ad onto the publisher/platform. It's the natural fit when the goal is traffic or conversions rather than awareness.

The price paid per video view, where a 'view' is defined by the platform — often 30 seconds watched, completion, or an interaction (whichever comes first). Common on YouTube and other video platforms.

Why it matters: CPV aligns spend with actual video engagement rather than mere impressions, so you only pay when someone genuinely watches. Essential for judging the efficiency of video and CTV campaigns.

The cost of acquiring one conversion — a sale, sign-up, or other defined action. The advertiser pays only when the desired outcome happens, making it the most performance-focused pricing model.

Why it matters: CPA maps spend directly to business results, so it's the metric that connects advertising to ROI most cleanly. Marketers compare CPA against the value of a customer to judge whether a campaign is profitable.

A form of CPA specific to lead generation — the cost of acquiring one qualified lead, such as a completed contact form or newsletter sign-up. Common in B2B and high-consideration purchases.

Why it matters: For businesses where the sale happens offline or over a long cycle, the lead is the measurable outcome. CPL lets those advertisers buy media on a results basis even when the final sale can't be tracked directly.

The cost of driving a single app install. The standard pricing model for mobile app-install campaigns, where the tracked outcome is the download and first open of the app.

Why it matters: App marketers live and die by CPI versus the lifetime value of a user. It's the headline efficiency metric for user-acquisition campaigns across app stores and in-app ad networks.

The percentage of impressions that result in a click. It measures how effectively an ad prompts people to act — a direct read on creative and targeting relevance.

Why it matters: CTR is the single most-watched engagement metric in display and search. A low CTR signals weak creative, poor targeting, or banner blindness; a high CTR (in search especially) also improves Quality Score and lowers costs.

The percentage of clicks (or visits) that complete the desired action — a purchase, sign-up, or download. Where CTR measures interest, CVR measures follow-through.

Why it matters: CVR reveals how well the post-click experience — the landing page and offer — turns interest into outcomes. You can have a great CTR and still fail commercially if CVR is poor.

The percentage of video ads played to completion (or to a defined point). VCR measures how many viewers watched all the way through rather than skipping.

Why it matters: For video and CTV, completion is the core engagement signal — it tells you whether your story is holding attention or losing it at the skip button. Strongly tied to brand recall.

The percentage of served ads that were actually viewable — by the IAB standard, at least 50% of the ad's pixels on screen for at least one second (two seconds for video). An ad can be 'served' without ever being seen.

Why it matters: Viewability separates ads that had a chance to make an impression from those that loaded below the fold and were never scrolled into view. It's a quality gate buyers increasingly insist on before paying.

The publisher-side mirror of CPM: the revenue earned per thousand impressions or pageviews. The headline figure in AdSense and other publisher dashboards.

Why it matters: RPM is how a publisher judges how well their inventory monetises. It bundles fill rate, CPM, and ad density into one number you can track and try to improve over time.

A normalised CPM that lets you compare earnings across campaigns sold on different models (CPC, CPA, CPV). It converts whatever was actually earned back into a per-thousand-impressions figure.

Why it matters: Because inventory is sold so many different ways, eCPM is the great equaliser — it answers 'what is this placement really worth per thousand impressions?' regardless of how the deal was priced.

The revenue generated for every unit of currency spent on advertising. Expressed as a ratio or multiple — e.g. a ROAS of 4 means £4 of revenue per £1 spent.

Why it matters: ROAS is the bottom-line measure of whether advertising is paying for itself. It's the metric marketing leaders and finance teams use to judge whether to scale a channel up or cut it.

Reach is the number of unique people who saw an ad; frequency is the average number of times each person saw it. The two are always read together.

Why it matters: Too little frequency and the message doesn't stick; too much and you waste spend and irritate people (ad fatigue). Managing the reach/frequency balance is central to brand campaign planning.

The automated auction that decides which ad fills an impression, run in the milliseconds while a page loads. Advertisers bid programmatically on each individual impression based on the user and context.

Why it matters: RTB is the engine of programmatic advertising — it allocates billions of impressions efficiently and lets advertisers buy precisely the audiences they want, one impression at a time.

The software advertisers use to buy ad inventory programmatically across many exchanges and publishers from one interface — setting targeting, budgets, and bids. Examples: DV360, The Trade Desk.

Why it matters: The DSP is the buyer's cockpit. Understanding it explains how a single campaign can run across thousands of sites with unified targeting, bidding, and reporting.

The publisher-side counterpart to a DSP: software publishers use to offer their inventory to many buyers at once and maximise the price each impression fetches. Examples: Google Ad Manager, Magnite.

Why it matters: The SSP is how publishers plug into programmatic demand. Together, DSPs and SSPs meet at the ad exchange to form the programmatic marketplace.

An IAB standard — an XML schema that tells a video player where to fetch a video ad, how long it runs, when a skip button appears, and which tracking events to fire.

Why it matters: VAST is what makes video ads interoperable across players and platforms. Any time you see a pre-roll with a skip countdown, a VAST tag is orchestrating it behind the scenes.

A plain text file a publisher hosts at the root of their domain listing which companies are authorised to sell their ad inventory. An anti-fraud standard from the IAB.

Why it matters: ads.txt combats domain spoofing — buyers can verify that inventory claiming to be from a site is genuinely authorised. It's required for AdSense and most programmatic demand (AdDeck has one at /ads.txt).

The percentage of ad requests that are actually filled with a paying ad. When no advertiser bids high enough (or at all), the slot goes unfilled — lowering fill rate.

Why it matters: Fill rate is a key publisher health metric: unfilled impressions earn nothing. Low fill points to weak demand, overly high price floors, or inventory quality issues.