A word cloud is a visible representation of the most commonly used words in a block of text. The more often a word is used (relative to the others), the larger the font used for that word. A common use for this technique is the tag cloud (as seen in the sidebar area to the right).
Recently, I discovered this article on D&D word clouds. It compares the word clouds created by the core rule books for various editions of D&D, specifically, the difference in 4e compared to the others.
Hereafter are copies of the images used in that article:
Advanced Dungeons & Dragons
As you can see from the images above, each of the first five word clouds are very similar. The word cloud for 4e, on the other hand, is noticeably different. Read what you will into that. I interpret the difference as an example of the shift in the core tenets of the game.
Making A Word Cloud
I wanted to make my own word cloud so I looked around on the net to see what I could find. A quick search turned up this word cloud generator. You can enter a block of text or enter the url to a site that generates an RSS feed.
Here is the word cloud generated by my feed: