It lets you clear the bash command history, either completely or selectively. Here's the GNU docs for the history builtin: https://www.gnu.org/software/bash/manual/html_node/Bash-History-Builtins.html#index-history

(I'm not too familiar, someone else can clarify: is this available outside bash?)

What's interesting to me is the -a option, which lets you "flush" the history for the current session without ending the session. I can see that being useful!