Just like in math class, these are Cartesian coordinates (x, y, z) used to tell location in the game. Global coordinates correspond to a fleet's location in the universe, while local coordinates correspond to a fleet's location in a system.

A block of Global coordinates or local coordinates is 3 consecutive numbers. You can use them for copy pasting into navigation screens. Usually for parsing, rally points addition, or just one time fleet command.

ie: 9393445, -233445, 103343

The distance of a single coordinate digit is 4,000 km.

Also see Local Coordinates