In Greek mythology, an Ethiopian princess whose mother Cassiopeia boasted that she herself (or, in some stories, her daughter) was more beautiful than the nereids. In revenge Poseidon sent a sea monster to ravage the country; to placate him Andromeda was fastened to a rock and exposed to the monster, from which she was rescued by Perseus.
Andromeda is also the name of a large northern constellation between Perseus and Pegasus, with few bright stars. It is chiefly notable for the Andromeda Galaxy (or Great Nebula of Andromeda), a conspicuous spiral galaxy probably twice as massive as our own and located 2 million light years away.
Andromeda strain a hypothetical, novel type of micro-organism, especially one created by genetic engineering, whose release into the environment could cause widespread destruction of life. The phrase comes from the title of a book by Michael Crichton.