Rooted in the Church of Scotland, "Presbyterian" describes Christian churches that conform to a governmental structure involving "presbyters," or elders. These elders are a part of a structure that involves regional gatherings of churches, known as "presbyteries," and often regional gatherings of presbyteries, known as "synods." Each denomination known as "Presbyterian" varies somewhat in its particular governmental structure, but "Presbyterian" describes this congregational connection to a larger body as the primary feature of church government rather than a particular set of beliefs.
Beliefs vary widely among Presbyterian denominations. See their individual categories for more information on beliefs, specific church structure, and individual congregations.