Definition of cats and dogs:
(n) :
(chiefly in set phrases) A heavy rain; a large amount of rain.
(adv) :
(chiefly in set phrases, about raining, other precipitation, or leaking) Heavily; copiously; a lot.
(n) :
People or things that constantly fight (see fight like cats and dogs).
(n) :
(finance) Stocks that can be purchased cheaply but are unlikely to produce much profit.