As opposed to
spawn killing (when you repeatedly kill your opponents directly upon their
spawn), kill
spawning is when one spawns and immediately kills an enemy, out of extraordinary luck and/or crappy respawn-placements.
I was just walking about on Foundry, enjoying my cyber-existance as an Elite,
feeling good about the world, and some
red guy just spontaneously materialized and kill spawned me. Thank you,
Bungie.