A solar eclipse is a phenomenon in which the Moon obscures the Sun. Looking from the Earth, it almost looks as though the Sun is being eaten by something. This explains why the word "shoku," which means "eating," is used to describe an eclipse in Japanese. Apparently people of long ago thought a dragon was eating the Sun.
A solar eclipse occurs during a new moon when the Sun, the Moon, and the Earth are in virtually a straight line. Because the Moon follows an elliptical orbit, the distance between the Earth and the Moon is not always the same. If the Moon is close to the Earth, or in other words if the Moon appears larger than the Sun when viewed from the Earth, the Sun is completely obscured by the moon and a "total eclipse" occurs. On the other hand, if the Moon appears slightly smaller than the Sun then the Moon is completely surrounded by the Sun and an "annular eclipse" occurs in which a ring of light is visible.

On the globe at left we've plotted all the areas on the Earth where total solar eclipses will be visible in the 21st century. The yellow strips signify "total solar eclipses," while the orange strips signify "annular eclipses."

Incidentally, a lunar eclipse is a phenomenon in which the Moon is obscured by the Earth's shadow, and occurs when the Moon is on the opposite side of the Earth from a solar eclipse.