Dairy is a category of milk and milk products made from the milk of cows, sheep and goats.
In some parts of the world, milk from other milk-producing animals may be included.
Eggs are often lumped in with dairy in North America, if only because they are kept in chillers next to the dairy in North American supermarkets.
People in Asia were milk-drinkers, but the ancient Greeks saw drinking milk as something astonishing: one of their words for barbarians was "milk-drinkers" (galaktopotes).
Literature & Lore
The English word "dairy" was originally dey-ery. Dey meant a woman servant in Middle English.
Dairying was traditionally seen as women's work:
"'We forgot about the cow. Your mother and them other women did. Get yourself a bucket and go hunt up Dick's cow and milk her.'
The boy scuffled the ground with his toe.
'Leave 'im be', Summers said. 'Hell, a man don't like to do women's work.'"
--Guthrie, AB. The Way West. Franklin Center, Pennsylvania: The Franklin Mint. 1979. Chapter Three, p 34.