[jmj42]

From Wikipedia: "The nautical mile is a unit of length that is approximately one minute of arc measured along any meridian."

[deelowe]

Still doesn't answer "why." More specifically, why is it more advantageous to measure it this way versus some other way? Why do airplanes measure their speed/distance in knots? Why not cars, trucks, runners, and physicists?

[andyjohnson0]

Ships and airplanes traditionally navigate using latitude/longitude measurements. Since that coordinate system is based on degrees/minutes/seconds of arc, a length unit that uses the same system is more natural.

[snake_plissken]

You don't travel on along a great circle when you driving or running. But when you are flying and sailing long distances, you do.

[jtarrio]

It's just a convenient way to define a unit of length. Look up the original definition of the metre and you'll see that it's basically the same except for some constants.