OPcache

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If you issue a 'php version' command in your terminal session

php -v

You'll see something like this:

PHP 7.2.34 (cli) (built: Oct  1 2020 20:37:38) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies
    with Zend OPcache v7.2.34, Copyright (c) 1999-2018, by Zend Technologies

The Zend OPcache, or simply OPcache is the subsystem that caches PHP script compilation for speedier performance of PHP applications. It is part of the 'Zend Engine' - the runtime interpreter for PHP (compare with Facebook's deprecated HHVM).

While Zend Server is a proprietary product offered by Zend Technologies, the Zend Engine and OPcache are part of the core of the freely licensed PHP https://github.com/php/php-src