I guess they could have used kill or terminate.

Seriously guys, this is just normal computing language. The OS makers didn't invent it. It's just the easiest way to convey the ideas.

You have a process that spawns another process. That spawned process needs to be terminated because it is not working properly; there is some error. So you tell that first process to terminate that second process that was spawned.

that's a parent process killing it's child! omg how terrible! No it's just normal computing things. just search "kill process child fork" and you'll get tons of actual examples.