The term "moon phase" refers to the different appearances of the Moon as it orbits the Earth. These phases are caused by the changing angles of sunlight illuminating the Moon from our perspective. The main phases include the New Moon, First Quarter, Full Moon, and Last Quarter, each representing a distinct stage in the lunar cycle. The complete lunar cycle takes about 29.5 days, during which the Moon transitions through its phases. Observing these phases can help people understand the Moon's position in relation to the Earth and the Sun, as well as its impact on natural phenomena like tides.