Value of `#$` when loading elisp files

Question

What is the value of #$ when loading a file?

package.el generates files like:

;;; anzu-autoloads.el --- automatically extracted autoloads
;;
;;; Code:
(add-to-list 'load-path 
    (directory-file-name (or (file-name-directory #$) 
                             (car load-path))))

Context: I'm trying to profile files loaded by intercepting calls to load. https://github.com/jschaf/esup/issues/53