Effective Set

Effective privileges are those permitted privileges a process uses for a single security-related task. By default, the effective set is initially equal to the permitted set, but a program should turn the effective set off at the beginning of execution to prepare for privilege bracketing.

Privilege bracketing is the practice of turning the effective privilege set off, then turning on (making effective) only those privileges needed for a specific security-related task, and turning them off as soon as they are no longer needed. See "Bracketing Effective Privileges".