An explanation of a few terms that are used further in this text:
A 'sitting': the set of loaded data files, selected datasets, detector and image settings, background and reflection regions, fitting parameters, etc. The complete state of a session can be saved to a session file, and later loaded from it.
An internal data structure that is related to a disk file. A file contains one or more datasets.
A detector image and its associated metadata.
The two-dimensional data structure that contains intensities read from the detector.
A number (neutron count) associated with each image pixel, as measured by the detector.