Filter

A filter is a condition applied to a report so that only matching data is counted, narrowing the view without changing what was collected.

Two distinctions cause most of the confusion. The first is filter versus segment: a filter is a temporary condition on the report in front of you, while a segment is a saved, named definition of a group that gets reused and compared side by side. The second is the level the condition applies at: filtering on an event property keeps only the matching events, while filtering on a user property keeps every event belonging to the matching users, and one condition applied the two ways gives two different totals. More important than either, a filter that narrows the numerator but not the denominator silently breaks every rate on the page, so a filtered rate must always be read together with the population it was computed over.