A word cloud is a visual representation of information using words as graphics with meaning. The larger the representation of the word, the more significant or common that meaning is in your data. I have a word cloud called a tag cloud right here in my sidebar. It links to the blog posts that are represented by those tags.
You can create a word cloud for other things too. The graphic above is a word cloud that reprsents the words I used in that last several blog posts. It was created with a free service called Wordle.
Wordle is a Java application that runs in your browser. Just surf to the Wordle page and start creating.
Here is the Wordle version of the word cloud based on the latest blog posts here at HowTutorial.com. Click through and after the java loads you can see it dynamically draw:
The Wordle terms of service allow you to use your word clouds as your own for what ever you need them for.