An ambigram is an illustration of a word or phrase that changes depending on its orientation, or it could be that the word or phrase stays the same despite a change in orientation. Changing the orientation could mean rotating it 180°, or 90°, or flipping it as a mirror image, horizontally or vertically. It's a kind of optical illusion. The website Ambigr.am is where ambigram enthusiasts go to see them, learn about them, and show off their own ambigrams. There are constant discussions and competitions between those who craft ambigrams.
The most impressive page is the Hall of Fame filled with the best winning ambigrams ever. Click on each image to change the orientation (if it isn't already animated). If you can't read it, click on the title to remove the spoiler guard. These are really clever, and some even find novel ways to define "orientation." Who knows? It might imspire you to become an ambigramist. -via Metafilter
(Image credit: Otto)