7.1. Categories, Tags, and Custom Taxonomies

In WordPress, taxonomies are used to add a relational dimension to how you group elements together. Categories and tags are both used to group posts together, and indeed define the taxonomy for any given post once assigned. Core WordPress includes three taxonomies by default: categories, tags, and link categories. Each time you create a new category, tag, or link category, you are creating a term of that taxonomy. For instance, a category called Neighborhoods would be a term of the category taxonomy, while a tag named Fiji would be a term of the tag taxonomy.

While we’ve already talked about categories and tags at length in Chapter 2, what’s important to recognize is that categories are hierarchical in nature. Individual categories can have subcategories, and then those subcategories can have their own subcategories, and so forth. Tags, on the other hand, are not hierarchical but merely labels that you apply to any given post, regardless of which category the post is nested in. In this way, you can think of categories as buckets that are used to group posts together, whereas tags provide a much looser relationship between posts.

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Note:

Link categories—the third taxonomy type that WordPress includes—are not necessarily a deprecated topic in WordPress, but are not particularly relevant for our discussion on taxonomies. What’s more important is to recognize that they are officially a separate taxonomy type that happen to be included with core which you might see referenced in documentation from time to time. For more information on link categories, have a look in the Codex.

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Understanding the relationship between categories and tags in the context of taxonomy is central to developing a solid information structure for your website’s content. The more thoroughly you plan how your WordPress site should function from the standpoint of content and information structure, the more successful your site will ultimately be.