One of Rincewind's surfeit of academic titles.
Another relatively easy academic title to have, requiring, at present, remarkably little actual work. This position resulted from an ancient curse by a dying wizard that sounded very much like "May you always teach fretwork!".
However, it is interesting that the failed wizard Brian, in A Hat Full of Sky, confesses to Tiffany Aching that he actually did study fretwork at Unseen University. Is there a story yet to be told here?
Ironically, Rincewind has demonstrated a modest capacity for woodworking in The Last Continent, in which he handcrafted primitive beach sandals from wood each evening as a safety precaution. (They made his footsteps sound like two people, and could be left behind as a distraction if this failed to bluff the hostile Ecksian wildlife.) This could well make Rincewind better-qualified for this job than he is for the majority of his UU job titles.