A solar eclipse occurs when the Sun, Moon and Earth are on a single line with the Moon in the middle. Seen from the Earth, the Moon is in front of the Sun and thus part or all of the light of the Sun is eclipsed by the Moon. Thus it may seem that a piece has been taken out of the Sun, or that it has suddenly disappeared.

There are four types of solar eclipses:
A partial solar eclipse: Only part of the Sun and the Moon overlap
A total solar eclipse: All of the Sun is hidden by the Moon
A ring-formed or annular eclipse: A ring of the Sun can still be seen around the Moon (caused by the Moon's umbra failing to reach the Earth's surface, which can happen if the Moon is near apogee). This is similar to a penumbral eclipse.
A hybrid eclipse: The curvature of Earth's surface causes a single solar eclipse to be observed as annular from some locations but total from other locations. A total eclipse is seen from places on the Earth's surface that lie along the path of the eclipse and are physically closer to the Moon, and so intersect the Moon's umbra; other locations, further from the Moon, fall in the Moon's antumbra and the eclipse is annular.

Solar eclipses can be more logically described as occultations. They can only happen during the new moon lunar phase.

Source: Wikipedia.org

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