There are multiple definitions:

1. ultrafast Papanicolaou(English)

   • stain used in evaluating solitary pulmonary nodules
   • MPR, SPN
   • Pulmonology, Diagnostics
   • https://doi.org…hest.124.5.1985

2. ultrafine particle(English)

   • EPA, FPM, HEI, HRV, NRC, PAH
   • Air pollution, Atherosclerosis /atherogenic, Cardiology
   • https://doi.org….307.5717.1858a