Aggregation (or aggregate) filters are applied to the results of aggregations, which are applied on a per-group basis. For example, the triage view is grouped by fingerprint by default and so aggregation filters are applied to aggregations applied on every group. The explore view allows the user to put all results in one group or group by arbitrary attributes.
Aggregation filters will be supported in flame graphs in an upcoming release.
Aggregation filters will not be supported in the debugger or list views, as those use selection queries that have no aggregates.