This tune is from the Highland song of the same name, Mhic Iarla nam bratach bàna. Bratach Bàna is the title of a traditional, mouth music, waulking (working, fulling) song written in Gaelic thought to originate from the Isle of Barra in the Outer Hebrides, Scotland.
Literally, Bratach Bàna means "of white flags" or "of white banners". The words are taken from the song's first line "A mhic Iarla nam bratach bàna" which means "O son of the Earl of the white banners".
Waulking songs are Scottish folk songs, traditionally sung in the Gaelic language by women while waulking cloth. This practice involved a group of people beating newly woven tweed rhythmically against a table or similar surface to soften it. Simple, beat-driven songs were used to accompany the work. A waulking session often begins with slow-paced songs, with the tempo increasing as the cloth becomes softer. As the singers work the cloth, they gradually shift it to the left so as to work it thoroughly. A tradition holds that moving the cloth anticlockwise is unlucky.
Typically one person sings the verse, while the others join in the chorus. As with many folk music forms, the lyrics of waulking songs are not always strictly adhered to. Singers might add or leave out verses depending on the particular length and size of tweed being waulked. Verses from one song might appear in another, and at times the lead singer might improvise to include events or people known locally.
The chorus to many waulking songs consists of meaningless vocables, serving a function similar to 'tra la la' or 'hey hey hey' in other song forms.