What EXACTLY is an Unbeliever?

1 Cor ch. 6 vs 14Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?15And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?16And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people.17Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you.18And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty.

So what is an unbeliever exactly? What do you call someone who is not exactly born again, but beleives in God? what do you call someone who was once born again but got choked by the things of this world?

And are all these people the same as someone who has never believed in Christ?

And are all THESE people the same as someone who knows God exists but rejects him?

Because James said even the demons believe! And they tremble! So are demons unbelievers?

Someone tlak to me