There are three distinct formats of The set in Scottish Country Dancing:
While Round the room sets are for variable numbers of Dancers in a single, large Set, the specific format of each Longwise set and each Circular set defines the number of Dancers needed in order to perform the particular dance in the prescribed way. If a dance has Sets of, say, 3 Couples, it cannot be danced with fewer and so, for example, only two Sets can be made from eight Couples. However, in the most common format, the 3 Couple repeat in 4 couple set, only three Couples are dancing at any time and so dances with this type of Set can, at a pinch, be performed with three Couples if four are not available.
In some dances, especially those in which every Dancer in The set performs much the same Figures, the sequence of Figures is usually performed only once. More commonly, the sequence is repeated so that each Partner group in turn performs the principal part one or more times in succession while the other Partner groups perform the supporting parts; the process by which each Partner group becomes the principal Partner group is called the Progression.
During a dance, Partners often become separated but they are usually re-united by the end of the Repeat. In Caddam Wood, which has the 5 Couple repeat in 5 couple set format, the Original Couples remain separated even at the end of the first Repeat and are not re-united until the end of the dance. In Ardailly Mill, which has the Round the room set format, the Partner group consists of one Man and two Ladies; while the two Ladies remain as Partners and, indeed, have not Progressed at the end of the Repeat, each Man Progresses anticlockwise one Place and so the Original Partner groups are unlikely to be re-united. Progressive sets covers in more detail these rarer situations in which Partner groups break up into their constituent Dancers or The sets breaks up into their constituent Partner groups after which these components form new Sets ready for the next Repeat.
In most cases, the Dancers Finish in the Places in which they started. This does not apply in Round the room set formats; it does not apply to the 3rd and 4th Couples in 2 Couple repeat in 4 couple sets when danced formally; and, strangely, the devisers of the 5 Couple square set dance, Spiffin', chose not to apply this convention.
Where a dance involves Repeats, the sequence of Figures is usually prescribed by the deviser for a single Repeat, only. When describing the sequence of Figures in the current Repeat of a dance in the most common format, the 3 Couple repeat in 4 couple set, and also in the 2 Couple repeat in 4 couple set, there is often ambiguous usage of the expression, The set, to exclude those Couples who are awaiting a later Repeat. The Beginner can easily be confused by this and so a good teacher should make it clear which usage s/he means. Where it is necessary to be unambiguous in this Dictionary of Scottish Country Dancing, the group of Dancers prescribed for the dance will be called the Full set; the subset of those Dancers who actually perform in the current Repeat will be called the Active set.
In the detailed descriptions, the most common forms are explained with at least an allusion to the exceptions known to the author. Like spoken languages, Scottish Country Dancing has developed and will continue to do so, with the result that significantly different derivative or innovative forms may arise and may become much more commonplace.