The grouping of words in the lower left hand sidebar of this site is called a "tag cloud". The cloud shows you all the tags we are using on this site.
Tags are a new style of search data that describe what each page or story on the site is about. The tag cloud is therefore a visual map of the content on a site. Tags that are large and bold are written about a lot, tags that are smaller have only been written about a few times. Click on a tag and you get a search page showing you all tbe content on that topic.
Tags are a new form of information design pioneered by the most successful online communities. They offer another way to navigate content on a site, showing patterns, the scope of content available, and how popular different keywords are.
Some sites allow you to tag content with your own words, helping you organize and remember content that is relevant to you. And by sharing your tags with others, an evolutionary "wisdom of crowds" map is created, helping you and others find valuable signals within all the noise.