What does APO stand for?

Aeropro

Automatic Payment Order

American Community Properties Trust

Apache Point Observatory

Advanced Planning Optimizer

Alpha Phi Omega

Advanced Planner Optimizer

Apogee

 That point in a terrestrial orbit which is farthest from the Earth.  OR On an elliptical orbit path, the point at which a satellite is farthest from the Earth. OR The most distant point from the centre of the earth to an orbit around it

Amateur Philatelists Organization

Armenian Philharmonic Orchestra