Synodic month

A Synodic month is the average period of the Moon's revolution as measured relative to  the line joining the Sun and Earth. The moon orbits the Earth and because the Earth is oribiting the Sun at the same time, the moon must travel a distance further than an orbit of the Earth to return to a position with the same angular distance from the Sun

The Moon is often characterized by its phases and the phases of the moon are defined by the synodic month