Metric
A quantitative measure in a report, such as sessions, users, revenue or event count.
What makes it wrong.
The mechanism, not the warning.
Some metrics are not additive across rows or dates. Users is the standard example: the users of two weeks is not the sum of each week's users, because the same person appears in both. Summing a deduplicated metric always overstates.
In detail.
Metrics carry definitions that differ between systems using the same word. Users in analytics and reach in an advertising platform both mean distinct people and are counted by entirely different mechanisms, over different populations.
Comparing them directly is the most common cross-system reporting error, and it is one a shared vocabulary makes worse rather than better.
Where this is measured.
Metric comes from Google Analytics 4. The server page lists every tool that returns it, with its parameters.