The length of time during which a body in the solar system makes one orbit of the Sun relative to the Earth, that means that it returns to the same elongation: Because the Earth moves in its own orbit, the synodic period differs from the sidereal period, which is measured relative to the stars.

The synodic period of the Moon, which is called the lunar month, or lunation, is 29 1/2 days long which is longer than the sidereal month.

The synodic period is the time required for a body in the solar system to return to the same or about the same position relative to the Sun as seen from the Earth.

The Moon's synodic period is the time between successive recurrences of the same phase, that means the period between one full moon and the next full moon.