REVOLUTION

Motion of a celestial body in its orbit; circular motion about an axis usually external to the body. In some contexts the terms "revolution" and "rotation" are used interchangeably: but with reference to the motions of a celestial body, "revolution" refers to the motion in an orbit or about an axis external to the body, while "rotation" refers to motion about an axis within the body. Thus, the earth revolves about the sun annually and rotates about its axis daily.