| Abbreviation | Definition |
|---|---|
| PHW | Potable Hot Water |
| PHWC | Pseudo Horizontally Weakly Conformal |
| PHWR | Pressurized Heavy Water Reactor |
| PHWR | Pressurized Heavy-Water Reactor |
| PHYSICS | Painfully Hard Y Suddenly It Came Stressful |
| Phyy | Physics |
| PI | 3.1415926535 |
| PI | Penning ionization [ |
| PI | Perimeter Institute for Theoretical Physics |
| PI | Polarisation Index |
| PIB | Particle In a Box |
| PIC | Precision Ion Chamber |
| PID | Parameter Identication Data |
| PID | Photoionization detector |
| PIE | Possibility of Infinite Energy |
| PIF | Physics at the Information Frontier |
| PILAC | Pulsed Ion Linear ACcelerator |
| PIMA | Photonic Ionization Manipulation And Augmentation |
| PINS | Portable Isotopic Neutron Spectroscopy |
| PIP | Practically Instantaneous Propagation |