The CalFile is a calibration file originally created for use in the Ariel powder diffraction data reduction package.
Files using this format with the .cal extension are still used by several algorithms in Mantid.
The file is a simple text file with the following format
# number UDET offset select group
0 611 0.0000000 1 0
1 612 0.0000000 1 0
2 601 0.0000000 0 0
...
19 101001 -0.0497075 1 2
20 101002 -0.3515893 1 2
21 101003 -0.2803879 0 2
...
349 201001 0.0525040 1 3
350 201002 0.0538936 1 3
351 201003 0.0535027 1 3
...
See here for information on CalFile in the greater context of time-of-flight powder diffraction calibration.