Immortal,
supernatural creatures of
European mythology. This is a general category which includes beings such as
elves,
trolls,
gnomes,
goblins, and
dwarves. A legend of their origin claims that when
God expelled
Satan and his followers from
Heaven, some of the
fallen angels lodged in the
Earth instead of falling into
Hell, and became the faerie. It was considered bad to say "faerie", and they were referred to with euphemistic names like "
the little people".
Belief in the faerie apparently had its golden age around the 600s to 800s, IIRC. It declined as Christianity gained power in the Middle Ages and with the rise of rationalism, though there are still people who believe in them now. The Puritans considered them demonic. The cute flying Tinkerbell-esque "fairy" archetype came about mostly after the Renaissance.
The faerie were divided into two "courts", the Seelie, and the Unseelie. The Seelie were those which, while they could not be described as "good", were not evil. These faerie could be either "trooping" faerie traveling in groups, or solitary. Some faerie of this court would perform household chores as long as certain rules, often pertaining to what gifts to give or not to give, were followed. They tended to be mischievous. These faerie would try to steal babies and replace them with their own, which were called changelings. (They thought human children were more attractive.)
The Unseelie were evil solitary faeries. In stories, the Unseelie do things like placing a curse on a person who does the faerie a favor, and attempting to trick a man lost in the mountains into falling to his death. The redcap killed people and dyed his cap in their blood. One had to be wary of the Seelie and generally avoid them, but the Unseelie were to be feared.