nonce

From WordPress Codex:

<?php check_ajax_referer( $action, $query_arg, $die ) ?>

This function can be replaced via plugins. If plugins do not redefine these functions, then this will be used instead.

Verifies the AJAX request to prevent processing requests external of the blog.

Nonces should never be relied on for authentication or authorization, access control. Protect your functions using current_user_can(), always assume Nonces can be compromised.

$action

(string) (optional) Action nonce

Default: -1

$query_arg

(string) (optional) where to look for nonce in $_REQUEST (since 2.5)

Default: false

$die

(boolean) (optional) whether to die if the nonce is invalid

Default: true

Return Values

(boolean) 

If parameter $die is set to false this function will return a boolean of true if check passes or false if check fails