The Scottish Gaelic for such a tune is port a beul: "a tune from a mouth—specifically a cheerful tune—which in the plural becomes puirt à beul". In mainland Britain they are usually referred to as puirt a beul but a variety of other spellings and misspellings also exist, for example port-a-beul, puirt a bheul, puirt a' bhéil, etc. These are mostly due to the fact that a number of grammatical particles in Gaelic are very similar in nature, such as the definite articlea', the prepositions "of" and to" which can both be a and the preposition á "from" which can appear without the acute accent.
Modern Irish dictionaries give port(aireacht) béil, translated as "mouth music" also referred to as lilting. Older dictionaries, such as Dinneen, only give portaiḋeaċt, portaireaċt, or portonaċt.
Puirt à beul has sometimes been used for dancing when no instruments were available. Although some people believe that puirt à beul derives from a time when musical instruments -- in particular bagpipes -- were unavailable because they were banned, there is no evidence that musical instruments were banned by the Disarming Acts or the Act of Proscription 1746. In his book Traditional Gaelic Bagpiping 1745-1945, John Gibson reprints the entire Disarming Act of 1746 (which is the act usually blamed for the proscription of bagpipes), and shows that bagpipes were not banned. This in and of itself does not clarify whether or not musical instruments were taken away from the people.
Usually, the genre involves a single performer singing lighthearted, often bawdy lyrics, although these are sometimes replaced with meaningless vocables.
In puirt a beul, the rhythm and sound of the song often have more importance than the depth or even sense of the lyrics. Puirt a beul in this way resembles other song forms like scat singing. Normally, puirt are sung to a 4/4 or 6/8 beat. Performances today may highlight the vocal dexterity by one or two singers, although four-person performances are sometimes made at mods.
Some elements of puirt a beul may have originated as memory aids or as alternatives to instrumental forms such as bagpipe music.
We also have puirt a beul or mouth music - songs in which the rhythm of the words is meant to replicate the rhythm of certain dance tunes. Some of these songs may have been composed to assist fiddlers, and occasionally pipers, in learning a tune. Others may have been composed as a means of remembering tunes when the playing of the bagpipes or fiddle were proscribed or frowned upon.
When they came across the ocean the ancestors of modern Scottish Americans brought their music with them, including mouth music, which was often incorporated into the lyrics of songs. It became an integral part of Appalachian music, roots music, and bluegrass, from where it spread into many forms of American music.
^Watson, A. (2001). The Essential Gaelic - English Dictionary. Birlinn.
^Graham, Katie; Spadaro, Katherine M. (2001). Colloquial Scottish Gaelic: the complete course for beginners. New York: Routledge. p. 176. ISBN0-415-20675-8. "'Puirt' is actually the plural of 'port'—a cheerful song."