Native
A feature, a native function, native class, or native constant, is called native, built-in, native PHP, or internal, when it is part of the standard installation of PHP. For example, ., dot operator for concatenation, or the stdClass class are native to PHP.
On the other hand, a feature is custom: that is, when defined by the developer or a PHP extension.
<?php
// This is a native function
$s = strtolower($s);
// This is not a native function : it comes from an extension
$rar_arch = RarArchive::open('latest_winrar.rar');
?>