| PI | Principal Investigator | - | Atmospheric Research Center |
| PI | Plugging Index | - | Computer Acronyms(common) |
| PI | Pollution Index | - | Computer Acronyms(common) |
| PI | Polydispersity Index | - | Computer Acronyms(common) |
| PI | Present Illness | - | Medical(slang) |
| PI | Present Illness | - | Medical(slang) |
| PI | Payload Interrogator | - | Organizations |
| PI | PaYload Interrogator | - | Organizations |
| PI | Pen And Ink (Document Update) | - | Organizations |
| PI | Preliminary Investigation | - | Organizations |
| PI | Principal Investigator | - | Organizations |
| PI | Procurement Item | - | Organizations |
| PI | Program Introduction | - | Organizations |
| PI | PolyImide - PolyIsoprene - Private Investigator | - | Astronomy |
| PI | P?li Language (ISO 639-1 Code) | - | Astronomy |
| PI | Pebi | - | Astronomy |
| PI | Principal Investigator | - | Business and Finance |
