What does "$td" stand for in the documentation of PHP's mcrypt extension?

Question

http://php.net/manual/en/function.mcrypt-module-open.php

<?php
    $td = mcrypt_module_open(MCRYPT_DES, '',
        MCRYPT_MODE_ECB, '/usr/lib/mcrypt-modes');

    $td = mcrypt_module_open('rijndael-256', '', 'ofb', '');
?>

In the documentation, it is described as an "encryption descriptor" in mcrypt_enc_get_iv_size()'s page, but that's as far as I got.

It's bugging me that it isn't $ed :(

Answer 1

"Twofish Descriptor"?

Description

This function opens the module of the algorithm and the mode to be used. The name of the algorithm is specified in algorithm, e.g. "twofish" or is one of the MCRYPT_ciphername constants. The module is closed by calling mcrypt_module_close().

Return Values

Normally it returns an encryption descriptor, or FALSE on error.