SP stands for the Extra Easy SP plan. It's a newer part of the plan if you've been away from SW for more than 18 months and it focuses on purely Speed and Protein foods.
Rather than foods being Super Speed, Super free, etc. now foods are all marked with an S for speed, a P for Protein or nothing (lol)
The SP plan gets you to eat each meal with 50% Speed food and 50% Protein foods on every plate of food.
You basically have to avoid potatoes, bananas, cherries, pasta, rice, yogurts, and some other fruit/veg I can't remember but don't eat them enough to be able to remember them
- and all synned versions of those foods.
Does that make it clearer?
I would get confused with SF... there are many people on here who don't know the newer plan and could be using SF to mean Super Free... but that's just me