A three sided sail is known as a Lateen sail or also a triangular sail. With a four sided sail one is only able to sail against the wind, but with a Lateen sail it is possible to sail more directly into the wind.
Like that! If it were sail as in I sailed a cross the sea you could put you are a sailor you can SAIL very well. But if it was sail as in the sail on a ship, you could put the SAIL on the ship was ripped. And so on. Hope I answered your question xx
1) What do you mean by sail extender? The rope to hoist (raise) the sail is called the halyard. The vertical beam supporting the sail is the mast, the horizontal beam supporting the sail is the boom. 2) It's called a SPRIT - see: Dictionary.com