Faries have a similar meaning to Faeries, but the word faery is often used to talk about the ancient mythical faeries, such as in folklore and literature. For example Edmund Spensers' epic poem 'the faerie queen'.
The faeries (spelled this way) tend to be a kind of 'grown up' faery. Some people believe they are descended from ancient gods. There is also a connection with druidism and also witchcraft (as in morgan-le-fey of Arthurian legend, though she was mainly a witch). They are also linked to earth spirits, and elementals, and there are many different types of faery such as tylwyth teg (kind of welsh imp), the sidhe (of Ireland) and the seelie and unseelie court (Scotland). An important point is that these are rarely described as having wings.
Whereas fairy is used for the fairies of disney and childrens stories - such as tinkerbell, and as in fairy tales, fairy god-mothers and flower fairies. They have wings and tend to be friendly, gentle and kind (faeries, on the other hand can have a bit of a dark side and you wouldn't want to offend them by confusing them with the fairies). Sometimes the term describes any magical creature, including goblins or gnomes: at other times, the term only describes a specific type of more ethereal creature or sprite. Various folkloristic traditions refer to them euphemistically, by names such as wee folk, good folk, people of peace, fair folk. Fairies are generally described as human in appearance and having magical powers. Their origins are less clear in the folklore, being variously dead, or some form of demon, or a species completely independent of humans or angels.
Much of the folklore about fairies revolves around protection from their malice. Although in modern culture they are often depicted as young, sometimes winged, humanoids of small stature, they originally were depicted quite differently: tall, radiant, angelic beings or short, wizened trolls being two of the commonly mentioned forms. One common theme found among the Celtic nations describes a race of diminutive people who had been driven into hiding by invading humans. When considered as beings that a person might actually encounter, fairies were noted for their mischief and malice, as with faeries.
Be careful not to mix them up with pixies. Other types of faries are brownies, imps, sprites(though are commonly associated with pixies), puck, hobgoblin and gnomes. Though there are various other types, I don't think I would be able to write every single one of them down!
