What is a taxonomy?
Taxonomy is one of those words that most people never hear or use. Basically, a taxonomy is a way to group things together.
For example, I might have a bunch of different types of animals. I can group them together according to various characteristics and then assign those groups names. This is something most people encounter in biology classes, and it is known as the Linnaean Taxonomy.
In WordPress, a “taxonomy” is a grouping mechanism for some posts (or links or custom post types).
Category
The ‘category‘ taxonomy lets you group posts together by sorting them into various categories. These categories can then be seen on the site by using ‘/category/name‘ types of URLs. Categories tend to be pre-defined and broad ranging.
Tag
The ‘post_tag‘ taxonomy is similar to categories, but more freeform. Tags can be made up on the fly, by simply typing them in. They can be seen on the site in the ‘/tag/name‘ types of URLs. Posts tend to have numerous tags, and they are generally displayed near posts or in the form of tag clouds.