Last-click attribution
In practice, for a UK buyer
The paragraph above is the neutral answer. This is the part a vendor glossary leaves out.
It reliably over-credits search and retargeting and under-credits everything that created the demand they harvested, which is why a business optimising purely on last-click tends to shrink towards its existing customers. It is not useless — it is a consistent operational signal — but it cannot answer whether a channel was incremental, and no amount of modelling on top of it turns it into an answer.
What this one connects to
Most confusion in media buying comes from two adjacent terms being used interchangeably, so these are the neighbours worth reading next.
Attribution
Assigning credit for an outcome to the advertising touchpoints that preceded it, according to a rule the advertiser chose. A description of correlation in a conversion path, not a demonstration that the advertising caused anything.
Incrementality
The share of an outcome that happened because of the advertising, measured against what would have happened anyway. Measured by comparing an exposed group with a comparable unexposed one, not by counting conversions that followed an advert.
Retargeting
Showing advertising to people who have already interacted with a brand — visited a site, abandoned a basket, opened an email. Depends on being able to recognise the same person again on a later occasion.
CPA
The cost of one completed action, whether that is a sale, a lead or a booking, calculated by dividing spend by the actions attributed to it. That makes it entirely dependent on the attribution model underneath.
More on measurement and evidence
What you can prove afterwards, and the difference between a number that means something and a number that does not.
45 minutes. Bring a real brief and we compile it live. You describe one audience and watch it compile into seven targeting specifications, each with the score for how much of the definition survived.
Talk it through