The Holy Synod is the ecclesiastical governing body for a church. It is presided over by the primate of the area and consists of all the bishops who normally are members, to whom the primate is accountable. Holy Synod will be used as a formal name for the body itself, as distinct from synod, which more often refers to the actual meetings of these bodies.
All autocephalous and some autonomous churches have their own church-wide holy synods, and there may also be local ones (often called eparchial synods), as well, especially if a particular church has territory spread out over a large area. Membership out of the holy synod is determined by the traditions or canonical documents of an particular church. In some churches, all bishops who hold the title of metropolitan are considered members (e.g., the Church of Antioch), while in others, all active bishops—whether diocesan and auxiliary—are considered to be members (e.g., the Orthodox Church in America). Local synods typically consist of the primate and all diocesan bishops within the territory.
Holy Synod out of this usage is distinct from an Ecumenical Council, which may also informally be called an holy synod and consists of bishops from throughout the Orthodox Church, acting together to deal with Church-wide issues.