Tag clouds have become a fascinating at-a-glance method of representing data. In this case, we see the words that Barack Obama has emphasised due to repetition.
Tag clouds began as a navigational aid for websites. Here’s a live example representing the content of the many thousands of pictures and photographs stored on Flickr itself. Each word is a link with the most common words given greater prominence.
I’m not sure which tool these used – if you want to generate your own, one such tool is Wordle.