Wiktionary
n. A design that may be read as the same word, name or phrase (or sometimes two different words, names or phrases) when oriented in two different ways, usually when reflected along a vertical or horizontal axis or when rotated through 180 degrees.
Wikipedia
An ambigram is a word, art form or other symbolic representation whose elements retain meaning when viewed or interpreted from a different direction, perspective, or orientation.
The meaning of the ambigram may either change, or remain the same, when viewed or interpreted from different perspectives.
Douglas R. Hofstadter describes an ambigram as a "calligraphic design that manages to squeeze two different readings into the selfsame set of curves." Different ambigram artists (sometimes called ambigramists) may create completely different ambigrams from the same word or words, differing in both style and form.
Usage examples of "ambigram".
For an instant he felt the familiar collision of thrill, privilege, and dead fear that he had experienced when he first saw the ambigram this morning.
John Langdon, who rose brilliantly to my impossible challenge and created the ambigrams for this novel.
To one of the most ingenious and gifted artists alive, John Langdon, who rose brilliantly to my impossible challenge and created the ambigrams for this novel.
And although ambigrams were common in symbology-swastikas, yin yang, Jewish stars, simple crosses-the idea that a word could be crafted into an ambigram seemed utterly impossible.