The word zodiac comes from the Greek zodiakos meaning a circle. The root meaning of zodiakos comes from the primitive root zoad, meaning a path, or way. In this connection, it is used to denote the way in which the sun appears to move through the stars in the course of the year.
This course is repeated every year. The sun apparently returns to almost the exact spot that it occupied on the same date a year before. The path through the heavens along which the sun appears to travel is called the zodiac and is divided into twelve segments.
Each of these twelve segments is a well known group of stars called a constellation which will be familiar to most people. They are known as Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.
As with the Chinese zodiac, the sign under which you are born is thought to determine the type of person you are, what you like to do, how you react to events etc. Also the compatibility factor. Some signs are said to be much more compatible with each other than others. However, just because someone says that two signs don't get on astrologically, that does not mean they can't. Everyone is different and there are exceptions to any rule.