Query about ps command

["Sonawane, Rahul (Rahul)" <sonawane@avaya.com>]

Title: Query about ps command

Hi ,
         I have a query about the ps command.  Sometimes process ABC is shown as
                        root      9052     1  0 16:31 ?        00:00:00 /home/rahul/bin/ABC
        and sometimes it is shown as
                        root      9052     1  0 16:31 ?        00:00:00 [ABC]
        I would like to know what does the square bracket indicate. 

        Any information would really help. Thanks in advance.
Rahul