(blank) CROTAn EQUINOX NAXISn TBCOLn TUNITn AUTHOR CRPIXn EXTEND OBJECT TDIMn TZEROn BITPIX CRVALn EXTLEVEL OBSERVER TDISPn XTENSION BLANK CTYPEn EXTNAME ORIGIN TELESCOP BLOCKED DATAMAX EXTVER PCOUNT TFIELDS BSCALE DATAMIN GCOUNT PSCALn TFORMn BUNIT DATE GROUPS PTYPEn THEAP BZERO DATE-OBS HISTORY PZEROn TNULLn CDELTn END INSTRUME REFERENC TSCALn COMMENT EPOCH NAXIS SIMPLE TTYPEn
A concise definition of each of these is available from the
FWG html page:
http://legacy.gsfc.nasa.gov/docs/fcg/standard_dict.html