WordPress
WordPress
Also called WP.
WordPress is an open-source content management system written in PHP that stores its data in MySQL or MariaDB. You install it on your own host or use the hosted version at WordPress.com.
How it is measured
A site is core files (wp-admin, wp-includes, the root PHP files), your wp-content folder, and a database. Find the version with wp core version, in the wp-admin footer, or by visiting /wp-json/ and reading the namespaces. Minor security releases install automatically by default; major releases need approval or a setting.
Site Health under Tools > Site Health reports PHP and database versions, inactive plugins, and whether the REST API and loopback requests work. wp core check-update lists pending core updates.
Worked example
A small accounting firm runs WordPress 6.5 on PHP 7.4 with 14 plugins. Site Health shows a critical notice that PHP 7.4 is no longer supported. The host offers PHP 8.2 in the control panel.
On staging, switching to 8.2 produces three deprecation warnings from an old contact-form plugin and one fatal from a custom theme function. The developer fixes both, then switches production on a Sunday night.
How it differs
WordPress is the whole system, and wp-admin is the login-protected control panel inside it. A plugin and a theme are packages that extend it. WordPress.com is a hosted service, while WordPress software from wordpress.org is what you run on your own server and can modify.
Common errors
Running an old PHP version because it still works. Skipping minor updates. Keeping the default admin username and a weak password. Leaving unused plugins and themes installed. Confusing WordPress.com with the self-hosted software.
In practice
Run wp core version and wp plugin list today. Update to the latest minor release, remove the plugins you do not use, and check PHP in Site Health. Keep a tested backup before any major update.