In web design, usability describes the ease at which website users are able to fulfil the purpose(s) of the website. Usability is a fundamental aspect of web design that must be taken into consideration from word go.
If you arrive at a blog via one of it’s category pages, or navigate to a category page while browsing a blog, you’ll be met with a number of posts relating to a particular topic. However it may not be completely clear exactly what that topic is, without having to skim read a few of the posts. Single words and short phrases used as category links in your sidebar navigation might not be descriptive enough to properly sum up the content of the categories they link to.