>>758548
What is not heresy:
Having differences of opinion on non-crucial doctrine.
Belonging to a different denomination than the One True Church (TM), and I'm not just referring to Catholics here.
Being a non-Christian.
Catholics, Orthodox, Protestants, Lutherans, Anglicans, Baptists, Assembly of God, Church of God, Presbyterians, etc. are all generally NOT heretics, as they believe the words of Jesus and follow the Nicene Creed. Neither are neo-pagans, atheists, Buddhists, Orthodox Jews, or Hindus, because they don't claim to be Christians.
What is heresy:
Claiming to be a Christian while teaching doctrine contrary to core, Biblical teachings.
Jehovah's Witnesses are heretics because they believe Jesus was a creation of God, despite the opening of the Gospel of John.
Mormons are heretics because they believe God was man and that a man can become God.
Anybody who says "I am a Christian, but I believe there are multiple paths to God," is a heretic because they deny the words of Jesus that He is the only way to the Father and deny the necessity of His sacrifice.
There are some that could be argued either way, too. It's borderline heresy to say the Old Testament doesn't count, for example.