Multiplicity
Multiplicity refers to three or more star systems that are seen on Earth. They may be bound by real gravity, or simply because they are in the same direction when viewed from the earth, so they may be seen as near-universe multiplicity. The system that is actually bound by gravity is called a multi-system. The majority of the multiple sexes are triple sex, consisting of three separate groups. If it consists of four, it is called quartet, and when it consists of five, it is called quartet. In the triplet, the three stars revolve around their respective mass centers. Usually, the triple system is very closely attached to the two stars, forming a hierarchical structure in which the remaining stars revolve away from each other. Many other multiplicity of stars, as well as triplets, are forming a hierarchy.