The term 'moon unit' is composed of five words, each with a different number of letters. The first word is 'LEM, ' which stands for Lunar Excursion Module, a spacecraft used by the United States during the Apollo program to land on the moon. The second word is 'REAR, ' which refers to the back side of the moon, which is not visible from Earth. The third word is 'END, ' which indicates the END of the moon's orbit around the Earth. The fourth word is 'PHASE, ' which describes the different shapes of the moon as it orbits the Earth. The fifth and final word is 'BOTTOM, ' which refers to the lowest point of the moon's orbit. Together, these five words form the term 'moon unit, ' which is used to describe the entire lunar cycle.