Definitions of Pisces:

noun: a group of vertebrates comprising both cartilaginous and bony fishes and sometimes including the jawless vertebrates; not used technically
noun: the twelfth sign of the zodiac; the sun is in this sign from about February 19 to March 20
noun: a large faint zodiacal constellation; between Aquarius and Aries
noun: (astrology) a person who is born while the sun is in Pisces