A Moon Day (Lunar Day) is the period of time it takes for the Moon to complete one full rotation on its axis with respect to the Sun, and it is the time it takes the Moon to make one complete orbit around the Earth and come back to the same phase.
In lunar calendars, a lunar day is defined as 1/30 of a lunar month. Each month there's a different number of lunar days, from 29 to 30. Lunar days vary in duration, and can be as long as few minutes to over 24 hours.
Living synchronically with the Moon's cycles, knowing, and working with the energies of each lunar day, we can stay more in balance with the Universe, and live happier, healthier, more productive lives.