The PRODTYPE and PROCTYPE keywords are an NOAO convention for defining the type and reduction-level of image data products. PRODTYPE can have one of three values: 'image', 'dqmask' for a data-quality mask, and 'expmap' for an exposure map. The PROCTYPE refers to the level of data reduction applied to the file and can have the values: 'Raw' for the data as it was obtained at the telescope, 'InstCal' for instrumentally-reduced data, 'Resampled' for a calibrated and reprojected image, 'Stack' for a stack of two or more images, and 'MasterCal' for some form of master calibration (e.g. bias, dome-flat, etc) image.
Additional details are provided in the NOAO Data Handbook (http://ast.noao.edu/sites/default/files/NOAO_DHB_v2.2.pdf).