A “darkflat frameA "darkflat frame" is basically the same as a flat frame with the same exposure and camera settings, but shot in the dark. They are used to calibrate the flat frames. The combination/stack of multiple darkflat frames is called a "Master DarkFlat". More” is basically the same as a flat frameA "flat frame" is shot against a bright surface and contains vignetting and all the "bad" things (e.g. dust particles) that block/disturb your light train. The combination/stack of multiple flat frames is called a "Master Flat". More with the same exposure and camera settings, but shot in the dark. They are used to calibrate the flat frames. The combination/stack of multiple darkflat frames is called a “Master DarkFlat“.