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