@fansy,
Its usually a metal framed conservatory garden (like a big greenhouse. Its usually attached to great houses and is more common in UK than US. Several winter gardens exist. Im familiar with the town center in Toledo Oh, The Longwood and LAdsuex Gardens in PA and Md, The NAtional ARboretum. The very rich would have them as features added onto thweir great homes and they would be heated by separate oil fired heating plants.
Usually, from the ones Ive seen, the owners have nothing to do with the work in their winter gardens.