The Wordpress current user’s password is hashed and stored in this global variable. It is set using the cookie in the pluggable functions set_current_user($id, $name='') and get_currentuserinfo() defined in [wordpress root folder]/wp-includes/pluggable-functions.php.
Plugin and theme authors need not use this variable, unless they are changing the hashing algorithm or changing the authentication system.
Back to the full list of global variables.
Technorati tags: user_pass_md5
