Custom Post Type is the ability to create new post types. Great, but what is a Post Type? WordPress has the ability to display different content types. Blog posts are categorized under post type Posts. A user can create a new Page under the Post Type Page. Attachments are a unique Post Type too.
WordPress default Post Types are:
- Post (Post Type: ‘post’)
- Page (Post Type: ‘page’)
- Attachment (Post Type: ‘attachment’)
- Revision (Post Type: ‘revision’)
- Navigation Menu (Post Type: ‘nav_menu_item’)
- Custom CSS (Post Type: ‘custom_css’)
- Changesets (Post Type: ‘customize_changeset’)
- User Data Request (Post Type: ‘user_request’ )
If you want to read more about Custom Post Type you can read the WordPress Codex page