Tags are usually one- or two-word (three at the most) descriptions (or keywords) of a blog post. For example, I might tag this article “define tags” and “define categories”. The tags you choose are used by sites like Technorati (the blog search engine) to find your site and group it according to tags (e.g., putting all the posts with “define tags” into one link).
Lorelle at Lorelle on WordPress says:
Think of tags as a form of interactive yellow pages. The tag link takes you to a collection of posts tagged with that tag category name.
For instance, instead of going to a search engine and typing in the keywords for Nature Photography, you would click on the Nature Photography tag on the site you are visiting, which would then display a categorized listing of posts about Nature Photography.
Tags on your site can have two functions.
- Tags can link to related tag categories on Technorati or other tag sites, showing a collection of offsite posts from around the web all related to the tag category, such as Nature Photography.
- Tags can link to a generated page such as your searches do, listing all of the posts on your site related to that specific tag.
Categories are a way for you to group your posts on your own blog. You can name categories anything you like and those categories may be unique to your blog (e.g., I have a friend who has a category called I think it’s funny. You probably won’t find that in a tag-related site or on another blog for the most part.)
Please read the rest of Lorelle’s article on Categories versus Tags – What’s the Difference and Which One? She provides information about the differences between tags and categories as well as when to use each.
Additional articles of interest on tags and categories: