Definicija: Rain having a pH less than 5.6. The acidity results from chemical reactions occurring when water, sulphur dioxide, and nitrogen oxides, generally released by industrial processes, are chemically transformed into sulphuric and nitric acids.

Definicija: Dež s pH, manjšim od 5,6. Kislost je posledica kemične reakcije, ki nastane, ko se voda, žveplov dioksid ter dušikov dioksid (največkrat produkt emisije, industrijskih procesov) kemično vežejo v žveplovo ali dušikovo kislino.