A lot of people have been debating back and forth lately about post formats and custom post formats. This discussion also gets all confused with post types, and custom taxonomies, and categories, and tags… It’s time for some clarity. Mark had a really good post on the topic, but I think this needs to be explored in more detail.

Custom Post Types: These were poorly named. Think: Custom Content Types. That is, non-post content. Examples: employees, products, attachments, menu items, pages, pets. If you want it to show up in your site’s main RSS feed, then it’s probably not a custom post type.

In general, taxonomies are used to arrange, classify and group things. By default, Taxonomies in WordPress are tags and categories that WordPress is using for the posts. Apart from these two, WordPress makes it possible for theme developers to create their own taxonomies which are created within the functions.php theme file. This is what we are going to cover today. We will learn how to work with Custom WordPress taxonomies.

Finally, WordPress version 3 gives us fully hierarchical custom taxonomies. Notice how the hierarchical nature allows us to simplify the Operating System taxonomy, for instance, by pushing all the different Windows variants under a “Windows” parent classification. This will allow visitors to see all posts classified with any Windows operating system, or allow them to be more specific and see only posts classified with Windows XP, for instance.

In this guide, we’ll go through the process of creating and using your own custom post type. More specifically, we will create an "Event" post type for your special events and dates, sort of like a calendar.

A custom taxonomy is exactly what it sounds like — a custom way to relate disparate content together. Custom taxonomies can be applied to custom post types or to regular pages and posts.