While listening to the radio yesterday, it occurred to me that I had no idea what a hotbed was. I've heard the phrase a thousand times (usually in relation to sin), and it turns out that I've seen them too. I simply didn't know what they were.
A hotbed is a flowerbed enclosed in a glass case. This bed is heated, usually by the fermentation of manure, to make a flowerbed that is hot and therefore good for growing things in (but not, unfortunately for sinning in).
Here is a diagram:
As you can see, there is little room for those who like their sins spacious. There is, though, another sort of hotbed. Apparently in the cheapest of cheap American lodging houses one can, or could, be given a bed that was used by different people in rotation. The hotness here is the same hotness that warms a hot-desk, and is ideal for sinners.
Neither hotbeds nor hot-desks, though, have much to do with a hotseat, which was, originally, the electric chair.