Advanced Process Notes - Parent/Child relationship

Every process has a Parent process. (Exception: the very first process, called "init").

"ps". Eg:  ps -o pid,ppid,command 
pstree

nohup'd and disown'ed processes get re-parented to init
processes send a "SIGCHLD" signal to their parent when stopped or terminated. (ignored by default).

A Zombie is a process that has terminated, but the parent process has neither "disowned" nor "reaped" the child. A zombie has finished executing, so it can't be sent signals.