Computing, and Unix in particular, is rife with metaphor.
The main metaphor for processes is that of a living being which is born, lives and dies.
In Unix all processes except init have parents, and any process which spawns other processes has children. Processes may become orphaned (if their parent dies) and can even become zombies, if they hang around after their death.
Thus, the kill command fits in with this metaphor.
It can be used to signal gently to a process that it should terminate itself (sending a SIGTERM which can be caught and handled gracefully) or it can be used to pull the rug out from under a process (kill -9 sends a SIGKILL which cannot be caught).