A stellium is a cluster of three or more planets in conjunction in a zodiac sign. A stellium holds more importance than your Sun , Moon or Ascendant signs. In other words, a stellium represents a special quality about you. It indicates your passion or interest or gift that you have been given in life.
The quality of the sign where the stellium is present is manifested more in the native and the planetary ruler where the stellium resides rules more over the native. In other words, it is an obsession that takes over your identity.
A stellium is a very rare and unique phenomenon when a few planetary bodies come together in the sky. Astrology always gives greater importance to such a configuration. So when a person is born with a stellium in one of his natal houses he brings about revolutionary changes around. He has the ability to manipulate the situation or the atmosphere around.
Such people have the tenacity to end the old and mark the start of a new age or new vision. The sign where the stellium falls and the area of life which that house represents would be greatly highlighted.
Often, people with stelliums are born into families that need a new lease of life, a new, different and revitalizing soul to end the old patterns, break away with conventions of the past and start a new karmic cycle for the whole clan or even participate in social/global new innovations and ideas.
Natives with stellium need enough confidence and courage to trust their own selves and start getting into action. Usually such people start to make a difference between their 30 and 40 years of age.
They become inspirational figures, innovators, rule- breakers, and great creators. However some natives with stellium also are found to release this new-found energy by way of addictions of sorts and end up the wrong alley. Having three or more planets in a single house usually makes the native very agitated, restless and frustrated. Some of them may end up in depression. It is best if natives with stelliums give up worldly possessions and end up in spiritual path.
Do note that stelliums are very common. Generally the planets and Venus are very close to each other and this combination would be close by to the Sun. Where this combination is posited matters a lot.