By - Freakyjoestarman
A killbox is a designated location that forces your enemy into an unfavorable position and allows your forces to more easily overpower/kill them.
In Rimworld, this usually means a large boxed in location with a single narrow entrance that raiders can freely charge into that forces them to bottleneck and March single file while your colonists/turrets wait in well defended positions to gun them down en masse with relative safety.
A killbox is a method of dealing with raiders. It involves having a base that is completely surrounded by walls; on the edge of one of these walls (our on multiple walls; you can have many killboxes though this imo lowers their efficiency) you place a rectangular area mostly enclosed with high walls. On the side of the rectangle closest to your base, you will have defenses for your colonists to hide and shoot behind like sandboxes or short walls. On the opposite end of the rectangle, you have a single entrance leading into a long, looping hallway.
In between these two points, you will ensure that there are no trees or shrubs or rocks for enemies to take cover behind. The idea is to have enemies slowly trickle into this box where your colonists will have superior cover so that they can mow down enemies safely.
How to get enemies to come into your killbox? There are no doors keeping enemies out- from the start of the long hallway, all the way across the open field, past your colonist's cover, their should be a direct path into your base; you can put a door there to keep animals out during normal periods, but as soon as normal raiders drop, that door needs to be opened. The majority of enemies (depending on difficulty) will have AI that prioritizes going into your killbox because they "see" that there is an unobstructed path straight into your base.
Now, killboxes are controversial to some people. Those people will often say that killboxes are a) abusing the AI and/or b) turtling amd ruining the difficulty of the game. Other people will say that on very hard difficulties of the game, killboxes are necessary for survival.
Nonetheless, I believe with 1.3 or 1.2, Tynan created more diverse raids specifically to counter this strategy- namely the enhanced breach raids that will ignore your killbox and make their own entrance in a place more inopportune for your colonists.
If you're interested in killbox design, this is a good video explanation: https://youtu.be/K8fsjNjbz8Y
Did you google "rimworld Killbox"? it will give you nice visual representations and explanations.
They enter box, they get the die
I have this whole box of kill and a charitable disposition.
Tldr it’s where you funnel enemies and have all your defenses ready