The current (or last) event that each session is waiting for. In 10g and above, this info is also visible in v$session.
Columns ___________________________ SID SEQ# EVENT P1TEXT P1 (Parameter 1) P1RAW P2TEXT P2 (Parameter 2) P2RAW P3TEXT P3 (Parameter 3) P3RAW WAIT_TIME SECONDS_IN_WAIT STATE
Related:
V$ACCESS V$DATAFILE V$MYSTAT V$PROCESS V$SESSION V$SESSION_CONNECT_INFO V$SESSION_CURSOR_CACHE V$SESSION_EVENT V$SESSION_LONGOPS V$SESSION_OBJECT_CACHE V$SESSTAT V$SESS_IO