This guide will show you how to change the “Advanced” options for your taxonomies. You can find this by visiting the Taxonomies screen and editing a taxonomy.
The first four options on this screen control the public settings for this taxonomy. If you uncheck the “Public” box, this taxonomy can only be used in the admin area of your website.
The “metabox callback” is for the metabox that appears when editing a post.
“Default Term” allows you to load a default term that will be visible whenever a new post is created.