Native

A feature is called native or built-in 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');

?>

See also https://www.exakat.io/en/the-100-php-functions-in-2022/

Related : Userland