When processes are managed, two concepts come up, they are the Real and the Effective ID of the process. To detail the difference, you have to understand the Difference between setuid / setgid / sticky bits.

The Real ID is the ID of the user that started the process, suppose that the process was started by program with setuid or setgid, this special permissions are from another user, that users ID is the so called “Effective ID”, the users ID whoes privileges where obtained by the setuid/setgid, basically, the owner of the executable.