|In astronomy, the term period usually refers to how long an object takes to complete one cycle of revolution. In particular the orbital period of a star or planet is the time it takes to return to the same place in the orbit. The spin period of a star is the time it takes to rotate on its axis.||
Alternately, a wave period is the time taken for one complete cycle of the wave to pass a reference point.
Here G is Newton's gravitational constant.