An ambigram is a word that looks exactly the same upside down as it does right side up. Specifically, if you rotate the image 180 degrees, it will look identical. In the image above, I’ve done some extra work for you… so now you don’t have to flip your head upside down in order to see the ambigram.
If you’re read or seen the DaVinci Code, you’ll see some references to ambigrams in the book and movie. I like this example because it is fairly simple, and you can instantly recognize what it is. Sometimes with ambigrams you look at the word and it is really difficult to read what it says in the first place, and the reason for that is most likely that they are using a word (or group of words) that just don’t really lend themselves to being a cool ambigram picture.