| CTF | Contrast Transfer Function. |
| RCT | Random Conical Tilt. |
| SNR | Signal-to-Noise Ratio. |
| Pixel | Information element in a 2D image. |
| Voxel | Information element in a 3D density map. |
| ROI | Region of Interest (in an image or a density map). |
| MOI | Moment of Inertia. |
| COM | Center of Mass. |
| PCA | Principal Component Analysis. |
| C.C. | Cross-Correlation coefficient. |
| I.A.N. | Image Analysis Network, the development team of PARTICLE. |
| GUI | Graphical User Interface. |
| CP | Control Panel (part of the program GUI). |
| DP | Display Panel (part of the program GUI). |
| VLDS | Very Large DataSet (containing multi-million particles). |
| GUI-Mode | Running the PARTICLE program with a graphical user interface. |
| CMX-Mode |
Running the PARTICLE program at the command line (with a CMX parameter definition file). |
| Visual Scripting |
Recording a GUI procedure to a command script that can then be used for data batch processing. |
| Master Image |
In tilt-pair or tilt-series data acquisition, the image recorded as the first exposure (normally containing better signal than the subsequent exposures). |
| Pair Image |
In tilt-pair data acquisition, the image recorded as the second exposure at a different, controlled tilting geometry. |