A Tag Cloud (or weighted list in visual design) is a visual depiction of user-generated tags used typically to describe the content of web sites. Tags are usually single words and are typically listed alphabetically, and the importance of a tag is shown with font size or color. Thus both finding a tag by alphabet and by popularity is possible. The tags made by the tag cloud creator are usually hyperlinks that lead to a collection of items that are associated with a tag.
Don't forget that your website's tag cloud can also help in optimising a website for major search engines - the tag cloud can function as a useful overview of a website by identifying important keywords associated with that website.
Tag cloud creating software usually builds the tag cloud list by crawling the pages in your website. There are also loads of other tag cloud software packages that will create special tag clouds, like linking to ClickBank products for example.
As well as linking to a website's pages, a tag cloud can also be generated from the users' search queries on a website, or from popular content stored in a database driven website. An example could be a financial website that shows a tag cloud of the most popular ticker symbols that were traded during that stock trading session.