Zombie Process
In plain terms
A finished process whose exit status hasn't been collected.
Going deeper
A zombie process has terminated but lingers in the process table because its parent hasn't read its exit status. It's dead but not cleaned up.
Under the hood
Harmless individually but accumulating zombies leak PIDs; the parent must 'reap' them via wait().
Examples
Process management, defunct processes, wait()/reap, ps showing <defunct>.
Think of it like...
Like a completed form sitting in the outbox because no one has filed it away.