A tag cloud or word cloud is a visual depiction of user-generated tags, or simply the word content of a site, used typically to describe the content of web sites.
Wordle is a toy for generating “word clouds” from text provided. The clouds give greater prominence to words that appear more frequently in the source text. Clouds can be tweaked with different fonts, layouts, and color schemes. The images created with Wordle can be used in many ways. Print them out, capture on screen, (easy with a Mac) or save them to the Wordle gallery to share with friends.