The term 'BIRD THAT DOESN'T FLY' can be summarized by the crossword solution of EMU, which is a three-letter word. An EMU is a large, flightless bird native to Australia and the second-largest living bird by height after the ostrich. It is a member of the ratite family, which also includes the ostrich, rhea, and kiwi. Emus are known for their long legs and powerful running ability, and they can reach speeds of up to 50 km/h. They are omnivorous, eating a variety of plants and insects.