In Irish and Scottish Gaelic folklore, the evil fairy host that flies through the air is called the Sluagh.
The Sluagh, also known as Sluagh na marbh—the “host of the dead”—were described as spirits of the unforgiven dead. Folklore from the Scottish Isles depicts them flying through the sky in a crescent formation, sometimes resembling a flock of birds. They could approach from any direction, seize a person, and carry the victim through the air from one island to another.
Although the Sluagh could occasionally rescue people trapped in dangerous places, they were generally feared as hostile or dangerous beings. Their association with death and night helped connect them with Halloween and other seasonal traditions concerning spirits returning to the human world.
The word comes from Old Irish slúag or slóg, meaning “host,” “army,” “crowd,” or “assembly.” “Fairy host” is therefore an English description rather than the proper Gaelic name. The Wild Hunt is a related spectral motif, but it is not the specific term asked for here.