| ARF | Ancillary Region File |
| CAL | Calibration Access Layer |
| CCD | Charge Coupled Device |
| CCF | Current Calibration File |
| CIF | Calibration Index File |
| EPIC | European Photon Imaging Camera |
| FITS | Flexible Image Transport System |
| GO | Guest Observer |
| GOF | NASA/GSFC Guest Observer Facility |
| GSFC | Goddard Space Flight Center |
| GUI | Graphical User Interface |
| HEASARC | High Energy Astrophysics Science Archive Research Center |
| HTML | Hyper Text Markup Language |
| OAL | ODF Access Layer |
| ODF | Observation Data File |
| OM | Optical Monitor |
| Portable Data Format | |
| PP | Pipeline Processing System |
| PPS | Pipeline Processing |
| PV | Performance Validation |
| RGS | Reflection Grating Spectrometer |
| RMF | Redistribution Matrix File |
| SAS | Science Analysis System |
| SOC | Science Operations Center |
| SSC | Survey Science Centre |
| SV | Science Validation |
| XMM | X-ray Multi-Mirror Mission |