What is a total solar eclipse?
A total solar eclipse is a phenomenon that occurs quite rarely. It occurs when the sun's lights or rays are totally blocked out by the moon in its orbital cycle around the earth. Since the moon is smaller that earth, the shadow it casts only partially covers the surface of the earth. Where the shadow is the darkest, its a total solar eclipse. Where the shadow only partially covers the sun, its called a partial eclipse.
visit : en.wikipedia.org/wiki/Solar_eclipse for more detailed info on this.