You have several preset post types in WordPress. A custom post type is a type that is not preset in WordPress.
Custom post type in WordPress
The default post types are page, article, and attachments such as images, videos, or other media files. If you need a different type of post for the content you want on the web, you can create one. You add it using the register_post_type function.
The custom post type will appear in the administration of your WordPress site as a new menu item. It will also have its own archive.