CALDB: Calibration Database
The CALDB is a Unix directory structure containing all the calibration data for Chandra, accessed via an index file. The index can be queried directly by most CIAO tools without the user having to know the location of the exact calibration file they need. In some cases, calibrations require user input, e.g. when there is a file selection required that the index cannot handle.
See the CALDB website for more information on the CALDB.