Below is a list of WordPress built in taxonomy names and built-in post type names. Never name your custom taxonomies and post types with one these to avoid collisions.
Taxonomies
category
— Categories (Posts)post_tag
— Tags (Posts)nav_menu
— Menu items (Appearance > Menus)post_format
— Post formats
Post Types
post
— Postspage
— Pagesattachment
— Media attachmentsrevision
— Post revisionsnav_menu_item
— Menu items (Appearance > Menus)
This information can also be found in the WordPress codex, but it’s rather buried and difficult to find. Hopefully this helps anyone looking for a quick reference to the names of WordPress built in taxonomies.