Categories and tags are examples of WordPress taxonomies. If you’re not familiar with the word “taxonomy A taxonomy is a way to group things together. In WordPress, some common taxonomies are category, link, tag, or post format. https://codex.wordpress.org/Taxonomies#Default_Taxonomies.”, don’t worry! Taxonomy is an academic discipline which defines groups of organisms that have shared characteristics and then names that group.
A taxonomy is a method of classification. WordPress comes with two default methods of classification:
Categories and tags are used to make it easier for your users to navigate your website. Used correctly, they can increase your website’s overall usability.
Each post must have one Category The 'category' taxonomy lets you group posts / content together that share a common bond. Categories are pre-defined and broad ranging., but it’s up to you whether you have Tags or not.
Some good advice is that your Categories are like your site’s table of contents, and your Tags are for your site’s index.
Categories is a hierarchical taxonomy. This means that you can create a tree structure, with parent categories and child categories.
For example, if you had the Recipes Category, you could have children such as Starter, Main Course, and Dessert.
Tags are a non-hierarchical taxonomy. This means that there are no parents and children, but the information is presented as flat. A post in the Dessert Category might have the tags baking, chocolate, cake, and nuts.
If you’d like to learn more about Categories and Tags, and how they work, you can read all about Taxonomies in the WordPress Codex.
Some developers will create Custom Taxonomies for use in their Themes or Plugins. These are simply other ways to classify your content. A Product Types taxonomy might be used for an ecommerce website, or a Portfolio Items taxonomy might be used for a web portfolio. You can read more about Custom Taxonomies in the WordPress Codex.