Did Q ever refer to it as such? It's been part of the general lexicon for so long that I can't even remember it's origin.

When was it first used? Why is it referred to as a killbox?

In military language a killbox is a 3D target area defined to facilitate the integration of joint weapons fire.

Was there anything that Q said that marked these bracket usages as such? Or was that an anon idea that took off?