WordPress at a glance
action is not described

profile_update action-hook . WP 2.0.0

Fires immediately after an existing user is updated.

Usage

add_action( 'profile_update', 'action_function_name_8640', 10, 2 );
function action_function_name_8640( $user_id, $old_user_data ){
	// action...
}
$user_id(int)
User ID.
$old_user_data(WP_User)
Object containing user's data prior to update.

Where the hook is called

wp_insert_user()
profile_update
wp-includes/user.php 1772
do_action( 'profile_update', $user_id, $old_user_data );

Where the hook is used (in WP core)

wp-admin/includes/admin-filters.php 117
add_action( 'profile_update', 'default_password_nag_edit_user', 10, 2 );