The process by which organisms excrete ammonia and ammonium ions in the form of nitrogenous waste substances is called ammonotelism.
Ammonia is the waste produced during the metabolism of nitrogen-containing compounds like nucleic acids and proteins.
Aquatic animals generally excrete ammonia into their watery surroundings directly, whereas terrestrial animals have evolved different mechanisms to eliminate the toxic ammonia from their body.
In vertebrate animals the major by-product of ammonia metabolism is urea.
While, in birds, terrestrial arthropods, and reptiles the major by-product of ammonia metabolism is uric acid.