Final answer:
MAR can refer to 'mare', which means 'sea' in Latin, used to describe large, dark, smooth areas on the Moon's surface that constitute about 17% of it.
Step-by-step explanation:
The abbreviation MAR may refer to different concepts depending on the context. If we are talking in terms of geography or celestial bodies, MAR can relate to the term mare, which in Latin means 'sea'. This term is specifically used to describe the dark, relatively smooth areas on the Moon's surface. These features are known as maria (plural for mare) and they cover about 17% of the Moon's surface, often being mistaken for actual seas by early astronomers due to their color and vastness.