sinposting aside, a denomination is basically a part of Christianity defined by a fairly homogenous set of ideals and ethics, church structure, and doctrine.
you have the main branches:
the apostolic churches (orthodoxy, catholicism, and a few ofshoots) are defined by direct succession from the original Apostles, meaning the church is uninterrupted from the time of Christ. orthodoxy, as the name implies, vales adherence to the original faith above all else. catholicism, as the name also implies, strives to be fully universal, even if that means some change happens to it.
you also have protestantism, split off from catholicism a while ago. they are defined by various degrees of traditionalism, lots of churches are unrecognizable from the apostolic ones, and, without apostolic succession, people have no qualms about founding their own churches. this has led to the 30000 churches meme. among them, some simply reject Rome's authority, preserving church structure and teaching to some extent.
then you have the shitshoe that are jehova's witnesses, mormons, and all the other cults.
they are not christian in any way, and act like proper cults, holding members in a collective prison were everyone is prisoner and guard at the same time
so, basically, anything except orthoxy is heresy and not worth your time.