What is `C-/` do in emacs?

Question

I recently mapped my Ctrl key to my Caps Lock key to make using emacs easier. Most of the time it is awesome but one unintended consequence is that C-/ is a frequent typo when I am going for the ? (i.e., SHIFT+/). When this happens I lose text and I can't undo it with C-z but I am not sure exactly what is happening.

What is C-/ doing?

Answer 1

Ctrl+/ runs the command undo. (unless it's been remapped)

You can always find out what a command does by asking emacs.

Ctrl+h k runs the describe-key function.
You type the above , enter a key sequence, and Emacs tells you what it does.