site personnel protection 
skeleton photoperiod 
skilled performance positivity 
skin perfusion pressure 
Small Periodic Perturbations 
small plaque parapsoriasis 
Small Power Producer 
SMI Premium Penalty 
Socially Prescribed Perfectionism 
Sociedad Peruana de Pediatría 
Society for Pediatric Pathology 
Society of Professional Pilots 
sodium pentosan polysulfate 
sodium pentosan polysulphate 
Software Portability Plan 
Southwest Power Pool, Inc. 
Space Power Plant 
Space power program 
Spatial Pattern Predictor 
Special Priority Payment 
Special process procedure 
Special Purpose Payment 
Special-Purpose Processor 
Specialty Powder Products 
Species Plantarum Project 
Specific Purpose Payment 
Specific Purpose Payments 
Speech Processing Peripheral 
Speed/Power Product 
sphingosine-1-phosphate