Celtic is a broad, pan-regional umbrella for the traditional and tradition-inspired music of the Celtic nations—primarily Ireland and Scotland, but also Brittany (France), Wales, Galicia (Spain), the Isle of Man, and Cornwall.
It is characterized by modal melodies (often Dorian and Mixolydian), lilting dance rhythms (reels in 4/4, jigs in 6/8, slip jigs in 9/8, hornpipes with dotted swing), and extensive ornamentation (cuts, rolls, crans, grace notes). Typical instruments include fiddle, wooden flute, tin whistle, uilleann pipes or Great Highland bagpipes, button accordion/concertina, bodhrán, Celtic harp, bouzouki (adopted into Irish music), guitar, and occasionally piano.
Vocal traditions range from unaccompanied sean-nós singing to narrative ballads in English, Irish (Gaeilge), and Scottish Gaelic, as well as Breton and Welsh. Modern "Celtic" often denotes both heritage styles and contemporary hybrids that blend folk with pop, rock, and ambient/new age aesthetics while retaining core melodic modes, dance forms, and timbral signatures.