The term 'HART' can refer to a variety of things. In the context of a crossword, it could refer to a DEER, STAG, BUCK, MOSS, male red DEER, or ex-senator Gary. A DEER is a hoofed mammal that typically lives in wooded areas and is known for its antlers. A STAG is a male DEER, while a BUCK is a young male DEER. MOSS is a type of small plant that grows in moist environments. Male red DEER are a species of DEER with reddish-brown fur. Ex-senator Gary is likely referring to Gary Hart, an American politician who served as a United States Senator from Colorado from 1975 to 1987.