Teat is an alternative word for a nipple or breast. In cattle, goats, etc, it is the projection from the udder through which milk is discharged. Teat is also used for the rubber mouth piece of a baby's feeding bottle. Teat is derived from the Old French or Dutch word, "tete". An alternative, but possibly not unrelated, would be the Welsh word "teth" or the Old English, "titt" which is still used as a slang term. 'Tittit' may also be used as a sign of impatience, though rarely.
The number of teats varies through the "mammal world" from 2 to 19 .