PPID

A processes PPID is its Parent Process ID or Parent PID. As the name suggests it is the name of the process which invoked the current binary as its child. Every process has a PPID >= 1 apart from init who's PPID is 0. If a process's parent dies it will automatically become a child of init, this avoids having any orphaned processes which in turns avoids zombies, other UNIX like operating system don't take this approach so have various zombie problems.