| BCF | Basic Calibration File |
| caldb | calibration database |
| CPF | Calibration Product File |
| FTP | File Transfer Protocol |
| GSFC | Goddard Space Flight Center |
| LHEA | Laboratory for High Energy Astrophysics |
| MeV | Mega ( ) electron Volts |
| NASA | National Aeronautics and Space Administration |
| OGIP | Office of Guest Investigator Programmes |
| PMT | Photomultiplier Tube |
| psf | Point Spread Function |