You can define categories on the Categories page in the administrative area, at yoursite.mirocommunity.org/admin/categories/. Categories are publicly visible and are listed in the navigation of the default theme. Although the Categories page will automatically update with new categories, it may take some time for newly added or deleted categories to appear properly in the list of categories elsewhere on the site.
You can create an unlimited number of categories, however, this may become unwieldy in the navigation drop-down. Categories are hierarchical, which means you can create sub-categories and sub-sub categories.
If a video is in a sub-category, it will automatically appear on the category page. So, for example, if you had a category "Trees" and sub-category "Willows" and marked a video as being in the "Willows" sub-category, that video would automatically appear on the "Trees" listing page.
You can add videos to categories on the video page, in the review queue, or on the bulk edit page. You can also mark an entire source as belonging to a particular category, which will then add all videos from that source to the given category.
Videos and sources can be placed in multiple categories.
Categories generate custom RSS feeds which you can subscribe to with a feed reader or plug into a widget.