The laoi (plural laoithe) belongs primarily to the Fenian or Ossianic tradition, where it describes the long narrative poems attributed to Oisín, Caílte, and other survivors of the Fianna. These poems were sung or chanted to simple melodic formulas and preserved stories of Fionn Mac Cumhaill and his warriors across centuries of oral transmission. The laoi differs from the more aristocratic filí tradition in its accessibility and its association with wandering storytellers rather than court poets. James Macpherson's Ossian poems, though controversial, drew international attention to this tradition and influenced Romantic poetry across Europe.

Laoi is a lay or narrative song-poem, often associated with the Fenian cycle. It is shorter than an epic but longer than a lyric, telling a specific story. Poets use laoi to preserve heroic deeds and moral lessons. The laoi is meant to be sung, with a strong rhythmic structure. It bridges the gap between oral storytelling and written poetry. Studying laoi reveals the narrative techniques of Irish verse, including dialogue, description, and pacing. It is a versatile form for conveying history and legend.