Emacs/readline bindings for Delete Word. Open up a bash shell, type in `foo bar baz`, then press ctrl-W twice.
'^W' is what would appear instead if you weren't in a readline/emacs editor, but instead a dumb line terminal. Thus, leaving '^W' behind makes it look like you didn't realize what you just corrected is still visible.
It's a joke. I've now explained and ruined it.