These are a bunch of "word vectors" (generated w/ word2vec https://code.google.com/p/word2vec/) put through a dimensionality reduction/visualization technique called T-SNE and then plotted in 3d. As far as what the clustering represents, check out T-SNE (http://homepage.tudelft.nl/19j49/t-SNE.html), but the short answer is--it's hard to say...

Here's a longer explanation from a webinar I did yesterday where I demoed this: http://www.youtube.com/watch?v=wmlj5uTUTFY (skip to 12:11 to get to the applicable section)