Activity reports are split into 3 types. "Current" reports show what is happening now, "Historical" reports display expensive queries that have previously run, and "10 Seconds" reports monitor activity for a 10 second period.
Reports for viewing requests, sessions, locks and transactions.
Reports for viewing queries that have cumulatively consumed the most CPU and I/O and run for the longest duration.
These reports take a 10 second snapshot of activity for virtual file stats, waits and latches, performance counters, and queries.