A synodic day (or synodic rotation period or solar day) is the period for a celestial object to rotate once in relation to the star it is orbiting, and is the basis of solar time.
The synodic day is distinguished from the sidereal day, which is one complete rotation in relation to distant stars and is the basis of sidereal time.
A lunar day is the time it takes for Earth's Moon to complete on its axis one synodic rotation, meaning with respect to the Sun. The synodic period is about 29.53 Earth days, which is about 2.2 days longer than its sidereal period.
Informally, a lunar day and a lunar night are each approximately 14 Earth days. The formal lunar day is therefore the time of a full lunar day-night cycle.