PMON (Process MONitor) is an Oracle background process created when you start a database instance. The PMON process will free up resources if a user process fails (eg. release database locks).
PMON normally wakes up every 3 seconds to perform its housekeeping activities. PMON must always be running for an instance. If not, the instance will terminate.
To speed-up housekeeping, one may also wake-up PMON (process 2 below) manually:
SQL> oradebug setmypid SQL> oradebug wakeup 2
|Glossary of Terms|