PHP uses what is called Semantic versioning. This means that each version number is split into 3 figures separated by a full stop:
Major Release.Minor Release.Patch Revision number.
If you are running a supported Major/Minor release BUT your patch revision is not the very latest available (8.1.0, 8.0.13, 7.4.26, 7.3.33) you should do all you can to get your PHP updated to the very latest release as patch releases very often contain vital fixes to recently discovered security vulnerabilities.
If you detected that there isn't a version 6 of PHP you'd be right in thinking this is a little odd. If you want to know why there isn't a version 6 of PHP just read about it here.
Just follow our getting started guide to determine what PHP version your website runs.
If you are already running up to date PHP on your web server fantastic! Why not now sign up to our PHP version notifications email to receive updates whenever new versions are released. This can keep you one step ahead of possible issues in the future.
By the way; there wasn't a PHP v6 - PHP advanced from version 5.6 to 7.0.