Ammonia (thing)

1. The common name for NH₃, a strongly basic, irritating, colorless gas which is lighter than air and readily soluble in water. It is formed in nature as a by-product of protein metabolism in animals. Industrially, it is used in explosives, fertilizer, refrigerants, household cleaning solutions, etc.
   
   
2. Ammonium hydroxide (NH₄+), a solution of ammonia gas in water.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.