Usually lines of three people facing the same direction. Some dances are done with all of the lines of three facing the same direction in a big circle around around the hall. Each threesome is like the spoke of a wagon wheel extending toward the center of the hall. Some dances are done with each threesomes facing another group of three to form sets of six. In this arrangement one threesome would be facing counterclockwise around the big circle and the opposing threesome would be facing clockwise around the big circle.
Trios are very useful in dance groups where their are more of one gender than the other.
The choreographic description of most dances tends to identify centers and ends of each line, rather than males or females. A Sicilian circle is formed by couples facing couples like spokes of a wheel in a large circle around the hall. They require a large group of people to be danced comfortably. At least 24 couples are needed to keep the radius of the circle large enough to permit couples to quickly identify the next couple in the big ring. Dances in a Sicilian circle formations can be called in the same style as squares or prompted like contra dancing.