Which unit is abbreviated as NM?

The unit abbreviated as NM refers to Nautical Miles. Nautical Miles are a standard unit of measurement used in maritime and air navigation to account for the curvature of the Earth. One nautical mile is defined as one minute of latitude and is equivalent to approximately 1.15078 statute miles or 1.852 kilometers. This unit is particularly important in aviation and maritime operations because it allows for more straightforward distance calculations over the surface of the Earth, especially when considering navigational charts and instrument readings.

This makes Nautical Miles the correct choice, as it aligns with the navigational practices and the specific measurements used in aviation, such as FAA regulations, which govern the operation of unmanned aircraft. The other terms listed do not correspond to the standard measurement used in aviation or maritime contexts.