The Chinese animal signs (Chinese Zodiac) are a 12-year cycle used for dating the years.
They represent a cyclical concept of time, rather than the Western linear concept of time.
The Chinese Lunar Calendar is based on the cycles of the moon, and is constructed in a different fashion than the Western solar calendar.
In the Chinese calendar, the beginning of the year falls somewhere between late January and early February.
The Chinese have adopted the Western calendar since 1911, but the lunar calendar is still used for festive occasions such as the Chinese New Year.
A popular folk method which reflected this cyclical method of recording years are the Twelve Animal Signs.
Every year is assigned an animal name or "sign" according to a repeating cycle: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Sheep, Monkey, Rooster, Dog, and Boar.
Therefore, every twelve years the same animal name or "sign" would reappear.
A cultural sidelight of the animal signs in Chinese folklore is that horoscopes have developed around the animal signs, much like monthly horoscopes in the West have been developed for the different moon signs, Pisces, Aries, etc.
For example, a Chinese horoscope may predict that a person born in the Year of the Horse would be, "cheerful, popular, and loves to compliment others".