Impressions on paper, framed or loose, made to hang on a wall: engravings, mezzotints, etchings, lithographs and woodblocks, sold singly and, very often, in pairs and sets.
Sets are the habit on Sellingantiques: 169 titles say pair, 84 say four, 29 say six, and one Regency lot runs to 27 hand-tinted sheets.