When Moon comes between the Sun and Earth, the shadow falls on the surface of the Earth. The Sun is entirely covered by the Moon for a brief period. Those places that are engulfed by the dark, dense umbral shadow of the Moon experience the total solar eclipse. In the regions that plunge into the soft diffused penumbral shadow of the Moon experience the partial eclipse. In all solar eclipse the Sun, Moon and Earth may not be perfectly aligned, and then we only have a partial eclipse. When the three celestial bodies happen to be in a straight line, we have Total solar eclipse.
"Annular solar eclipse is a particular case of the total solar eclipse. Like the total solar eclipse, the Moon is aligned with the Sun. However, on that day, the apparent size of the Moon happens to be a wee smaller than the Sun. Hence the Moon covers the central part of the Sun, and the rim of the Sun appear like a 'ring of fire' in the sky for a very brief moment" explains Samir Dhurde of The Inter-University Centre for Astronomy and Astrophysics, Pune.