Interesting. I have just realized that if I am talking about the installed structures, whether they be on a wall or under a counter, they are cabinets, but if I refer to them as storage spaces they are cupboards. My kitchen has brown cabinets, but the dishes are in the cupboard over the microwave. Otherwise, a cabinet is a free-standing piece of furniture with doors. It may have drawers as well, but if it has only drawers it's not a cabinet. A closet-like small room is always a closet, unless it's it's a pantry, which need not be small. I've never known such a room as a cupboard. I need to ask some friends about their usage.