CPC Cost Per Click
The average amount spent each time someone clicks an ad. A rising CPC on its own is not automatically negative; it needs to be read against conversion rate to know whether it reflects a real problem.
Cost metrics
These terms describe what a campaign spends and how efficiently it spends it. They are usually the first numbers a marketer looks at, and the ones most likely to be misread when viewed alone.
CPA Cost Per Acquisition
The average spend required to generate one conversion, however that conversion is defined for the campaign. Comparing CPA across campaigns only works when the conversion definition is the same in each.
ROAS Return On Ad Spend
A ratio comparing revenue attributed to a campaign against what was spent on it. The attribution model behind the number changes what counts as "attributed revenue," which is why ROAS can shift when a setting changes without spend changing at all.
Budget pacing
How evenly a daily or monthly budget is being spent across the period it covers. Uneven pacing can signal a bidding issue or a change in competition rather than a change in demand.
Performance and engagement metrics
CTR Click-Through Rate
The percentage of people who saw an ad and clicked it. It reflects how relevant or attention-getting the ad creative and targeting are, more than how well the campaign converts afterward.
Conversion rate
The percentage of clicks, or sometimes impressions, that result in a defined action. A strong CTR paired with a weak conversion rate often points to a mismatch between the ad and the landing experience.
Frequency
The average number of times a single person sees an ad within a given period. Rising frequency alongside falling CTR can indicate an audience is seeing the same creative too often.
Bounce rate
The share of sessions where a visitor leaves after viewing only one page. In GA4, this is reported differently than in earlier analytics tools, which is a common source of confusion when comparing historical data.
Viewability
The percentage of ad impressions that were actually visible on screen for a meaningful duration, as opposed to loaded but never seen.
Attribution and audience terms
These terms explain how credit for a conversion gets assigned, and how an audience gets defined behind the scenes. Attribution settings are one of the most common reasons two reports on the same campaign show different totals.
Attribution window
The length of time after an ad interaction during which a conversion is still credited to that ad. A shorter window can lower reported conversions without any real change in performance.
Assisted conversions
Conversions where a channel played a role earlier in the customer's path but was not the final interaction credited with the sale.
Quality or relevance score
A platform's internal estimate of how relevant an ad is to its audience and landing page, which can influence cost per click and ad placement.
Impression share
The percentage of available impressions a campaign actually received, compared against how many it was eligible to receive given budget and targeting.
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