What is the difference between Fly-By and Short-Turn?
The context of your question is a bit unclear, but assuming that you're asking about navigation waypoints in the US then you're probably referring to these terms as defined in the FAA's Pilot/Controller Glossary:


  FLY-BY WAYPOINT- A fly-by waypoint requires the use of turn
  anticipation to avoid overshoot of the next flight segment.
  
  FLY-OVER WAYPOINT- A fly-over waypoint precludes any turn until the
  waypoint is overflown and is followed by an intercept maneuver of the
  next flight segment.


As per the comments, I have never heard of a "short turn" waypoint and it isn't in the P/CG.