1. Decomposition or rotting, the breakdown of organic matter usually by bacterial action, resulting in the formation of other substances of less complex constitution with the evolution of ammonia or its derivatives and hydrogen sulfide; characterized usually by the presence of toxic or malodorous products; decay; decomposition.
2. The decomposition of organic matter; especially, the typically anaerobic splitting of protein by bacteria and fungi with the formation of foul-smelling and poisonous products; such as the ptomaines, mercaptans, and hydrogen sulfide.