Source : Webster's Revised Unabridged Dictionary (1913)

Hotbed \Hot"bed`\, n.
   1. (Gardening) A bed of earth heated by fermenting manure or
      other substances, and covered with glass, intended for
      raising early plants, or for nourishing exotics.

   2. A place which favors rapid growth or development; as, a
      hotbed of sedition.

Source : WordNet®

hotbed
     n 1: a situation that is ideal for rapid development (especially
          of something bad); "it was a hotbed of vice"
     2: a bed of earth covered with glass and heated by rotting
        manure to promote the growth of plants