Meters are the internal units used to measure distance in Neverwinter Nights. This applies to game data (such as spell ranges), scripts, and even the very areas themselves. (Areas are built from square tiles whose sides are 10 meters.)
Many humans are two meters tall, but this is a result of careful modelling and is not enforced by the game.
The unit is based on the SI unit of the same name, which is approximately 3.3 feet. Hence some in-game text will refer to distances in terms of "feet", with the same conversion factor (1 meter = 3.3 feet).