| Acronym | Meaning |
| PAC | Polycyclic Aromatic Compound |
| PAC | Perturbed Angular Correlation |
| PAC | Photoacoustic Calorimetry |
| PAC | Polyaluminum Chloride |
| PAC | Powdered Activated Carbon |
| PACAP | Pituitary Adenylate Cyclase-activating Polypeptide |
| PACE | Pacific Atmospheric Chemistry Experiment |
| PACE | Plasma Assisted Chemical Etching |
| PACIMS | Passive Chem. Ionization Mass Spectrometry |
| PACS | Physics And Astronomy Classification Scheme |
| PACT | Powdered Activated Carbon Treatment |
| PACT | Process Automation Configuration Tool [EPRI Software] |
| PACVD | Plasma-assisted Chemical Vapor Deposition |
| PAD | Pulsed Amperometric Detection |
| PADMR | Photoinduced Absorption Detected Magnetic Resonance |
| PADRE | Particle Analysis And Data Reduction Program |
| PADS | Photoacoustic Deflection Spectroscopy |
| PAE | Postantibiotic Effect |
| PAECE | Protective Action Evaluator For Chemical Emergencies |
| PAEP | Photovoltaic Array Environmental Protection Program |
| PAES | Positron-induced Auger Electron Spectroscopy |
| PAF | Platelet Activating Factor |
| PAFC | Phosphoric Acid Fuel Cells |
| PAFP | Photochemical Aerosol Forming Potential |
| PAFT | Program For Alternative Fluorocarbon Toxicology Testing |
| PAG | Periaqueductal Gray |
| PAG | Photoacid Generator |
| PAGE | Polyacrylamide Gel Electrophoresis |
| PAGE | Policy Analysis Of The Greenhouse Effect |
| PAGIF | Polyacrylamide Gel Isoelectric Focusing |
| PAGIRS | Pesticide Assessment Guidelines Information Retrieval System |
| PAH | Polycyclic Aromatic Hydrocarbon |
| PAHO | Pan American Health Organization |
| PAI | Pesticide Active Ingredient |
| PAI | Plasminogen Activator Inhibitor |
| PAI-1 | Plasminogen Activator Inhibitor 1 |
| PAIR | Patent Application Information Retrieval System |
| PAIR | Preliminary Assessment Information Rule |
| PAIRS | Program For The Analysis Of Infrared Spectra |
| PAIS | Public Affairs Information Service |
| PAK | P21-Activated Kinase |
| PAL | Positron Annihilation Lifetime |
| PALMS | Particle Analysis By Laser Mass Spectrometry |
| PALS | Positron Annihilation Lifetime Spectroscopy |
| PAM | Photolabile Attachment Molecules |
| PAM | Peptidylglycine Alpha-amidating Monooxygenase |
| PAM | Performance Assessment Methodology |
| PAM | Periodic Anderson Model |
| PAMBE | Plasma-assisted Molecular Beam Epitaxy |
| PAMPA | Parallel Artificial Membrane Permeation Assay |