hotbed

noun3

1. •
   A low bed of earth covered with glass, and heated with rotting manure, used for the germination of seeds and the growth of tender plants, like a miniature hothouse.

   • Tomato seedlings will be ready to transplant from the hotbed to the coldframe in 12 to 18 days after sowing the seed, depending upon the amount of sunshine and the care given the bed. — 1924
2. •
   An environment that is ideal for the growth or development of something, especially of something undesirable.

   • In particular, Kumamoto prefecture in southwestern Japan is quickly becoming a hotbed for tech investment from companies including TSMC and Fujifilm Holdings Corp (FUJIF). — 2023
3. •
   An iron platform in a rolling mill, on which hot bars, rails, etc., are laid to cool.