What counts a "kill"?

So I'm playing with the Stats through Kills mod this run, and it got me thinking: what counts as a kill for the player (for the mod or for general stat counting in case there's a difference)?

Obviously direct combat, but does a vehicle turret count? If I Molotov a house and a zombie walks in, does that count as my kill if they burn or if it collapses on them? If I stab a creature of one faction to near death but another creature finishes it, does that count?

I'm kind of curious how abstract I can get before the game stops giving me credit.