UNIX - Process State Codes
O - On processor -- the process is executing on the CPU in either user or system mode.
R - Runnable -- the process is on a run queue and is running or runnable.
S - Sleeping -- the process is waiting for a I/O event to complete.
Z - zombie -- process, terminated but not reaped by its parent.
T - stopped -- process has been stopped
X - dead -- (should never be seen)
For more information on process life-cycles click here