backward-sexp is an interactive compiled Lisp function in `lisp.el'.

It is bound to <C-M-left>, C-M-b, ESC <C-left>.

(backward-sexp &optional ARG)

Move backward across one balanced expression (sexp).
With ARG, do it that many times. Negative arg -N means
move forward across N balanced expressions.
This command assumes point is not in a string or comment.
Uses `forward-sexp' to do the work.