An ambigram is a word written / drawn so that it's legible in two directions - "normally" and upside-down. An example is the logo above - rotated 180 degrees, it's exactly the same.
Ambigrams don't necessarily have to be the same word both directions. For examples of many different types of ambigrams, I would highly recommend John Langdon's page. There are many types of wordplay examples there, phrases, and .. just go there.
Anyways, feel free to join and post any ambigrams / wordplay things you've done, links to ambigram pages, or questions about how to make ambigrams. Anything like that. This community is just starting out but maybe it'll grow someday.