Short answers, pulled from the story.
The word fairy derives from Old French faerie, which came from fae and the suffix -erie. Fae itself traces back to Latin fata, a feminine form of fatum meaning fate. It originally denoted a beautiful woman capable of using magic to influence human affairs, and the singular form fairy began replacing the collective use from the 14th century onward.
Before modern medicine, fairies were commonly blamed for tuberculosis, birth deformities, and unexplained illness. Consumption was attributed to fairies forcing people to dance at revels every night until they wasted away. Children born with abnormalities or developmental disabilities were often said to be changelings, fairy substitutes left in place of a stolen human infant.
In Scottish folklore, the Seelie Court consists of fairies more beneficently inclined toward humans, though still capable of harm if offended. The Unseelie Court comprises fairies who brought harm to humans for entertainment. Both courts were considered dangerous to provoke.
Common protective charms against fairies included church bells, four-leaf clovers, rowan trees, and clothing worn inside out. In Newfoundland, bread was the most popular protection, ranging from stale bread to hard tack to fresh homemade bread. A source from County Wexford, Ireland, recorded in 1882, noted that bread wrapped in an infant's clothing protected it when carried out after dark.
The Tuatha Dé Danann were a race of supernaturally gifted people in Irish mythology, regarded in ancient times as the main deities of pre-Christian Ireland. After being defeated by the ancestors of the Irish people, they were said to have withdrawn into the sídhe, or fairy mounds, where they lived on in popular imagination as fairies. They are associated with Otherworld realms including Mag Mell, Emain Ablach, and Tír na nÓg.
In his 1902 novel The Little White Bird, J. M. Barrie wrote that when the first baby laughed for the first time, the laugh broke into a million pieces that went skipping about, and that was the beginning of fairies. This origin story was later incorporated into his Peter Pan works, where the character Tinker Bell became a pop culture icon.