Core is a term used by developers. When the WordPress kernel is said, it means all the files that are in the basic installation (out of the box).
It is the code that runs the WP itself. We then extend it through plugins and themes.
What we mean by the term core
When you say core, you mean the files that power the current WordPress software. They come in every download of WordPress.
When you say the WordPress core team , it means a group of developers who are involved in creating new WordPress themes, updating them, and fixing bugs.
Was this article helpful for you? Support me by sharing, please. 👍