I still feel like these abbreviations "photlam" and "photnu" are very opaque--maybe this is just ignorance on my part, butthe only places I ever seen them used are in other, mostly older HST-specific calibration software, and they often are left undefined.  I think people only even know what they are because they're used as FITS keywords.  In fairness I don't have a better alternative..."photon flux density" is a mouthful.