Advertising terms explained

The words you'll meet buying UK advertising

Impression

A single instance of an ad being displayed to someone, counted whether or not it was actually noticed. A banner ad that loads on a news site racks up an impression the moment it appears on the page, even if the visitor scrolls straight past it.

Reach

The number of distinct people exposed to an ad, each person counted once no matter how many times they saw it. A campaign can rack up a large number of impressions while reaching a fairly small group of people, if that group keeps seeing the same ad repeatedly.

Frequency

The average number of times the same person sees an ad over a given period, used to judge whether a campaign is finding new people or repeating itself. A high frequency on a small audience often means budget is being spent showing an ad to people who have already seen it several times over.

CPM (cost per thousand impressions)

The price paid for every thousand times an ad is shown, the standard way of comparing cost across display and video placements. CPM lets a business compare a video ad slot against a display banner on a like-for-like basis, since both are priced per thousand views.

CPC (cost per click)

The price paid each time someone clicks an ad, used where the goal is getting visitors to a website or landing page. A search ad is typically bought on CPC, so the advertiser pays only when someone actually clicks through to their site.

CTR (click-through rate)

The proportion of people who saw an ad who then clicked it, a rough signal of how relevant the ad felt to the audience it reached. Two ads can have the same number of impressions but a very different CTR, which usually points to a difference in the message or the image.

CPA (cost per acquisition)

The average cost of getting one paying customer or completed action, worked out by dividing total spend by the number of conversions. A retailer running two campaigns side by side can use CPA to see which one is actually bringing in customers at a workable cost.

ROAS (return on ad spend)

The revenue an ad campaign generates for every pound spent on it, used to judge whether the spend is paying for itself. A campaign with a strong CTR can still have a poor ROAS if the clicks it attracts rarely turn into sales.

Conversion

The specific action an advertiser wants a viewer to take, such as a purchase, a form submission or a phone call, defined before a campaign starts so that costs can be measured against it. A campaign aimed at newsletter sign-ups and one aimed at direct sales will look completely different in cost per conversion, even if they reach the same audience.

Attribution

The method used to decide which ad, out of several a customer may have encountered, gets the credit when a conversion happens. A customer might see a display ad, then a social ad, then search for the brand directly before buying, and attribution is the rule that decides which of those gets counted.

Programmatic advertising

Buying and placing ad space through automated software, matching ad slots to audiences as the page loads. An advertiser using programmatic buying sets an audience and budget and lets the software find the placements.

Real-time bidding (RTB)

The auction that sits inside programmatic buying, where each individual ad slot is bid on in the moment, in the fraction of a second before a webpage finishes loading. Every time a page loads, an RTB auction runs behind the scenes to decide whose ad fills the space, all before the visitor sees anything.

DSP (demand-side platform)

The software an advertiser or their agency uses to buy ad space across many publishers at once, setting an audience and a budget. A DSP is where an advertiser tells the system who they want to reach and how much they want to spend, and the system does the buying across many different sites.

SSP (supply-side platform)

The equivalent software used on the publisher's side, offering their ad space into the same auctions so it can be sold automatically to whichever buyer values it most. A publisher uses an SSP to make their ad slots available to advertisers automatically.

Ad exchange

The marketplace where DSPs and SSPs meet, and where the actual auction between advertisers and publishers takes place. The ad exchange is the middle layer that lets a DSP's bid and an SSP's ad slot find each other without either side dealing directly with the other.

Retargeting

Showing ads to people who have already visited a site or app, aimed at bringing back a visitor who looked but didn't convert the first time. Someone who adds an item to a basket and leaves without buying is a typical retargeting audience, since they've already shown intent.

Lookalike audience

A group of new people a platform selects because their profile resembles an advertiser's existing customers, used to extend reach beyond people already known to the business. A business builds a lookalike audience from its customer list to find new people who share similar characteristics.

Viewability

Whether an ad actually had the chance to be seen, based on how much of it appeared on screen and for how long, which is a different thing from an impression, which only records that the ad was served. An ad loaded at the very bottom of a long page can rack up impressions without ever being viewable, if nobody scrolls that far down.

Above the fold

The part of a webpage visible without scrolling, treated as more valuable space because it doesn't depend on the visitor scrolling further. A banner placed above the fold is seen by everyone who loads the page, while one further down is only seen by those who keep scrolling.

Brand safety

Keeping an ad away from content that could damage the advertiser's reputation by association, such as pages carrying misinformation or extreme material. Brand safety settings on a DSP stop an ad from appearing next to content the advertiser wouldn't want their name associated with.

ASA (Advertising Standards Authority)

The body that enforces the UK's advertising rules and investigates complaints about ads across most media, from posters to paid social. A misleading claim in a print ad or a paid social post can both end up as complaints the ASA looks into.

CAP Code

The set of rules the ASA applies when judging whether an ad is legal, decent, honest and truthful. It's worth checking the current wording at asa.org.uk before relying on any specific clause, since the code is updated from time to time. A weight-loss ad claiming quick results without evidence behind it is the kind of claim the CAP Code is built to catch.

Ofcom

The regulator responsible for broadcast standards, working alongside the ASA specifically on TV and radio advertising. A complaint about the content of a TV ad break sits within Ofcom's remit as much as the ASA's, since broadcast carries its own set of rules.

Substantiation

The evidence an advertiser needs to hold before making a claim in an ad, so that the claim can be checked if the ASA asks for it. A claim that a product is 'clinically proven' needs the clinical evidence sitting behind it before the ad ever runs.