RWRP is shorthand for ‘Reverse Wound, Reverse Polarity’. This means that one of the pickups is wound in the opposite direction to the others and also has the opposite magnetic polarity. What this does is fatten up the tone when 2 pickups are used. It also removes most of the background hum found in singlecoils.
Non RWRP, or standard is when all the pickups are wound in the same direction and polarity. This makes an out of phase ‘quacky’ sound that is brighter with less bottom end and slightly quieter than RWRP when 2 pickups are used together.
All Singlecoil pickups can be wound either way for no extra charge.