Wiktionary
fat farm
n. (context slang English) A health club or resort running weight-loss programs.
WordNet
fat farm
n. a health spa that specializes in helping people lose weight
Wikipedia
Fat Farm
"Fat Farm" is a short story by Orson Scott Card. It appears in his short story collection Maps in a Mirror. Card originally published this story in the January 1980 issue of Omni magazine.
Usage examples of "fat farm".
That hedgerow, with its sunken lane behind, would be a deathtrap to cavalry, while an open meadow, bright with buttercups and rising towards a fat farm on a gentle hill, would be a place to avoid like the plague if French cuiraisseurs were in the area.