Real Dictionary

hotbed
countable noun: If you say that somewhere is a hotbed of an undesirable activity, you are emphasizing that a lot of the activity is going on there or being started there.

hotbed in American English
a bed of earth covered with glass and heated by manure, electricity, etc. for forcing plants
intransitive verb: to share a bed in shifts, so that it is always occupied
noun: a bottomless, boxlike, usually glass-covered structure and the bed of earth it covers, heated typically by fermenting manure or electrical cables, for growing plants out of season

hotbed in British English
noun: a glass-covered bed of soil, usually heated by fermenting material, used for propagating plants, forcing early vegetables, etc