An ambigram is a word image that can be read in more than one direction.
Many of the examples you can find on the Web are a name that still reads as the same name when you turn it upside down. (Do an image search for “ambigram”.)
But an ambigram doesn’t have to read the same way in each direction. There’s a clever one in the header image of ambigram.com, with an image that reads as “ambigram” or, inverted, as “website”.