There are two main ways to categorise WordPress blog posts, tags and categories, in this post I want to explain the difference between categories and tags.
In this post I want to explain the differences between category and tags.
What Are Tags & Categories?
Both are ways to group related posts together, if someone is interested in your post about a cat, drop it into a tag or category about cats and people can find more content on your site about kitties.
Adding a post into a cat or tag, adds it to the category page linking all the other posts together for example, I’m putting this post in General Blogging, you can also see it in this page http://neilm.wpengine.com//category/general-blogging
The Cook Book Analogy
The best analogy I have heard for the difference between categories and tags is the cook book.
Imagine the front of a cook book there are chapter listings with page numbers, think of categories are chapter lists. The chapters in our analogy are breakfast, lunch, dinner and snacks.
Now think of your blog post as a recipe, our post is a breakfast dish huevo rancheros, it is in the chapter / category breakfast.
At the back of the book is an appendix, the appendix lists all the recipes by their main ingredients, this is a tag and helps to give much more detailed information about a post. We would tag huevo ranchero with eggs, peppers, totillas etc.
Both do the same thing to help you find a recipe but they both do it in slightly different ways. Tag are more detailed where as categories are more general.
Do You Need Both?
Each post needs to go into at least one category, that is why there is a default uncategorized category that all posts are added to by default, but you do not need to use tags, they are optional.
What Is Best For SEO
Having both for SEO is best, it increases the number of indexed pages you have in Google. for each category or tag you add a new archive page is added, s there would be oursite.com/category/breakfast and oursite.com/tag/eggs, oursite.com/tag/tortillas. The more tags and categories we have the more keyword rich links we have.
Are There A Limit To The Number Of Tags / Categories
Technically no, but there is a suggestion to limit the number to no more than 15 for anti-spam and seo reasons.
Wrap Up – The Difference Between Categories And Tags
Further reading, here is what the good people at WordPress.com have to say on this subject Categories Vs Tags.