Plan. Chart covering a small area on a very large scale. There is no distortion, relative distances and positions being maintained.
Plan Position Indicator. See Cathode Ray Tube.
Plane Chart. Chart constructed on a supposition that surface of Earth is flat in charted area. Except for small areas at Equator it would be erroneous. Is not used in modem chart construction. Mercator charts were, at one time, called 'plane charts'.