Emacs: nesting exceeds `max-lisp-eval-depth'

From time to time I get a "nesting exceeds `max-lisp-eval-depth'" error.

• What does it mean?
• When I get one, is there something I can do, other than "killall emacs"?

Edit:

You can get the error if you evaluate:

(defun func ()
  (func))
(func)

However, in this case emacs remains responsive.