The Chinese Zodiac is based on a twelve-year cycle, each year being represented by a particular real or "folklore" animal. They are: Rat, Ox, Tiger, Rabbit (or Cat), Dragon, Snake, Horse, Sheep, Monkey, Rooster (Cock or Phoenix), Dog, and Pig (or Boar). Thus are the twelve Chinese "signs."
The Chinese system of Astrology holds that each new year begins early in the first calendar month on a New Moon and relates this new year to one of the twelve animals of the traditional Chinese Zodiac. Their (the particular animal's) qualities are thought to "animate" the year and color it with their individual and distinct natures. Further, humans born in a particular animal-"ruled" year are said to share certain common traits of that year's animal -- both positive and negative.