A rule or set of rules that determines how attribution (credit) for conversions is assigned to different touchpoints in the conversion path.
Platforms may differ widely in terms of how they report conversion credit for the same source. Different tracking methods can lead to dramatically different counts, and different attribution models will intentionally weight conversion attribution differently. This allows various touchpoints and their relation to each other to be understood.
Example: Google Analytics (GA4) will present attribution as Last-Click by default. This means the last interaction source of the traffic prior to conversion will be assigned credit. This may conflict with the conversion count from an ad platform that also understands who saw an ad, and may only assign credit to ads if the interaction was within a shorter or longer duration since engagement.