Revolution is the orbiting of one celestial body around another.
A revolution is also the single complete course of such an orbit. For artificial satellites, revolutions are figured relative to a given point on the planet's surface. Because Earth is spinning west to east, a spacecraft in a west-to-east orbit takes longer to complete one revolution than to complete one orbit relative to a fixed point in space. For example, the Space Shuttle may make 16 orbits of Earth in a day but only 15 revolutions.