Sean nós literally means old style. It is a highly-ornamented style of solo, unaccompanied singing.  Sean nós songs can be relatively simple, but many are long, highly stylised and melodically complex, and a good performance typically involves significant ornamental and rhythmic variation from verse to verse.

Styles vary around Ireland - generally corresponding geographically to the various dialects of Irish - from the relatively unadorned and nasal style of the north to the more decorated styles of the south and west.