The perigee is the closest the moon gets to Earth, while the apogee, on the opposite side of the moon's orbit, is the farthest away it moves from Earth. Perigee and apogee can be used to describe the orbits of other objects orbiting Earth, such as man-made satellites.
While the moon is usually described as being about 237,700 miles from the Earth, this is really an average distance. Throughout the year, the moon rests at different apogees and perigees from the Earth. In 2013, the farthest apogee was 252,581 miles, and the nearest perigee was 221,824 miles. These numbers differ every month because the moon's orbit is also slightly eccentric with frequent variations.
The apogees and perigees of the moon determine how high ocean tides rise. Very close perigees result in higher tides than usual.