WordPress at a glance
action is not described

pre_get_users action-hook . WP 4.0.0

Fires before the WP_User_Query has been parsed.

The passed WP_User_Query object contains the query variables, not yet passed into SQL.

Usage

add_action( 'pre_get_users', 'action_function_name_9029' );
function action_function_name_9029( $this ){
	// action...
}
$this(WP_User_Query)
The current WP_User_Query instance, passed by reference.

Where the hook is called

WP_User_Query::prepare_query()
wp-includes/class-wp-user-query.php 230
do_action( 'pre_get_users', $this );

Where the hook is used (in WP core)

Does not used.