Conversion
An action the advertiser decided to count as a result, recorded and attributed by the platform.
What makes it wrong.
The mechanism, not the warning.
Duplicate counting between browser and server events is the most common inflation. It shows up as a conversion count that exceeds what the order system recorded, and it is invisible in the platform's own interface, which reports both paths as one figure.
In detail.
A conversion is a definition before it is a number. Which events count, how they are deduplicated, and which touchpoint gets credit are all configuration, and all of them change the reported total without changing what people did.
The same underlying purchase can arrive through a browser pixel, a server-side event, or both, and whether that is one conversion or two depends on the deduplication key being sent correctly.