There are multiple definitions:

1. specific pathogen free(English)

   • ELISA
   • Veterinary medicine

2. sun protection factor(English)

   • UPF, PLE
   • Photonics, Dermatology

3. sphenopalatine foramen(English)

   • the PPF communicates with the nasal cavity via this foramen, located just anterior to the Vidian canal opening
   • HRCT, IOF, ION, ITF, MRI, PMF
   • ENT, Medical imaging
   • https://doi.org…3244-016-0498-1