Haha, that is a funny misunderstanding. "bisect" stands for bisect. It is a word. It means to cut in half. Because the command cuts the range of suspicious commits into two, then tests which half the problem started in.
I swear, I didn't come up with that myself, I read that somewhere else, but of course I don't have a source anymore 🙈 Maybe some git developer is a huge fan of wordplays?