Irish dance
Irish dance comes in several forms, which can broadly be divided into social dances and performance dances. Irish social dancing can be divided further into céilí and set dancing, though the boundaries between the two are rather indistinct. Irish set and céilí dances are usualy danced by couples arranged into formations (sets); frequently squares of four couples, but many other formations are found, also. Irish social dance is a living tradition, and variations in the way a particular dance is danced are found across the Irish dance community; in some places, dances are deliberatley modified and new dances are written.
Irish performance dancing is usually referred to as stepdance. Irish stepdancing has been recently popularized by the world-famous show "Riverdance" and its followers. Aside from public dance performances, there are also stepdance competitions in Ireland, the United Kingdom, and North America. Most competitive stepdances are solo dances, though many stepdancers also perform and compete using traditional set and céilí dances.
Irish céilí dance
Irish social, or céilí', dances vary widely throughout Ireland and the rest of the world. A céilí may be performed with as few as four people and as many as sixteen. The Irish word "céilí" has no precise English word that means quite the same thing; "party" is the closest English can come. These dances are meant more for socialization and fun than as an athletic and competitive form. But the céilí dances are still fast-paced and may be quite complicated. In a social setting, the céilí may be "called" -- that is, the upcoming steps are announced during the dance for the benefit of newcomers.
Some of the céilí dances are named after the traditional Irish tunes to which they are most-frequently danced, others after the region of Ireland they were developed in, and others indicate the kind of music and/or the sizxe of the dance. Most céilí can be done to any tune of the appropriate time (jig or reel). The céilí dances were heavily influenced by French quadrille dances, and many are danced in the same formation, but many are danced in longways sets or sets of different sizes. Céilí dances are among the ancestors of the North American square dance.
The name céilí dance was invented in the late 19th century by the Gaelic League, to distinguish non-quadrille dances from the quadrille-based set dances, which were thought to be a British or foreign influence in Ireland.
Irish set dances
Set dances are folk dances of Ireland based on French quadrilles, usually with four couples of dancers in a square. Set dances can be in any tempo of music, and sometimes will change from a reel to a jig part-way through. Set dances emphasize fancy footwork more so than ceili dances. Typically, a set dance is not danced all the way through; instead, each section is briefly talked through before dancing it.
Irish stepdance
Irish solo stepdances fall into two broad categories based on the shoes worn: hardshoe and soft shoe dances.
"Reel", "slip jig", "hornpipe", and "jig" and "set dance" are used to define dances, and also refer to types of tunes in Irish traditional music (and other traditional musics). Reels are tunes either in 2/4 or 4/4 time, with an even phrasing which distinguishes them from hornpipes. Slip jigs are in 9/8 time, and are considered to be the lightest and most graceful of the dances. Hornpipes can be in 2/4 or 4/4 time, with a triplet phrasing which distinguishes them from reels, and are danced in hard shoes. There are three jigs danced in competition, the light jig, the single jig and the treble (or double) jig. Light and single jigs are in 6/8 time, and are soft shoes dances, while the treble jig is hard shoe, danced in a slow 6/8.