Refers to how many times the copper wire is wound around each pole of the armature. Basic guide:
More Turns (e.g. 19T) = Higher torque, less rpm, longer battery life. Slower but easier to drive.
Less Turns (e.g. 12T) = Less torque, more rpm, shorter battery life. Faster but more difficult to drive.
Number of Winds
Besides the number of turns, the number of winds refer to the number of wires wound around the armature. Basic guide:
Single Wind = Most bottom end power. Power is achieved at lower rpms. For short racing tracks with a lot of turns.
Double / Triple / Quad = Less bottom end power. Power is achieved at higher rpms. For long racing tracks with long straights.
Turns refers to the number of times the copper wire has actually been revolved around the armature. The higher the number of turns greater is the torque generated and hence greater is the power delivered. However that also means less RPM rating for your rc car electric motor. Generally less turns are preferred for making the rc car run faster.
One or more copper wires are usually wound around the armature. The number of wires that are wound around the armature is called the wind of the motor. Sometimes the wind is increased in order to compensate for the torque lost by reducing the turns.
Stock motor is always 27-turn single-wind armature with the endbell keyed to 24° of timing (relation of the brushes in the endbell to the magnets in the can)
Super stock is a 19-turn single with (I think) adjustable timing (although most people just refer to them as a "nineteen-turn motor").