Categories and tags are two types of information that you can add to a blog post.
We use them to organize the information in your blog by topic and content (rather
than just by date), and to help visitors find what they are looking for on your blog.
Categories are primarily used for structural organizing. They can be hierarchical,
meaning a category can be a parent of another category. A relatively busy blog will
probably have at least ten categories, but probably no more than 15 or 20. Each post
in such a blog is likely to between one and possibly four categories assigned to it.
For example, a blog about food and cooking might have these categories: Recipes,
Food Talk, In The Media, Ingredients, and Restaurants. Of course, the numbers
mentioned are just suggestions; you can create and assign as many categories as
you like. The way you structure your categories is entirely up to you as well. There
are no true rules regarding this in the WordPress world, just guidelines like these.
Tags are primarily used as shorthand for describing the topics covered in a particular
blog post. A relatively busy blog will have anywhere from 15 to even 100 tags in use.
Each post in this blog is likely to have three to ten tags assigned to it. For example, a
post on the food blog about a recipe for butternut squash soup may have these tags:
soup, vegetarian, autumn, hot, and easy. Again, you can create and assign as many
tags as you like.