What is the core?#
The WordPress core is the main software you download from WordPress. Its two main folders are wp-admin and wp-includes, and files such as wp-login.php and index.php belong to it too. This part provides the dashboard, the editor, the database layer and the site's main logic.
What lives outside the core?#
The wp-content folder, which holds your themes, plugins and uploads, and the wp-config.php file, which holds the database connection settings. These are yours, and a core update does not erase them.
Example#
When WordPress updates to a new version, the core files are replaced. If you had manually changed something inside wp-includes, that change disappears.
The golden rule#
Never edit the core. To change behavior, use hooks, a child theme or a plugin.
Why do updates matter?#
Most core updates fix security issues. A long delay leaves the site open to known attacks. Small security updates usually install automatically.
Common mistake#
Downloading WordPress from unreliable sites or from a "modified translated version". Get the core only from the official source.
Back up before changes#
Before any major update, back up the files and database. If something breaks, restoring the previous version is simpler than troubleshooting in an emergency.