'Idol' in the Bible

Concerning therefore the eating of things sacrificed to idols, we know that no idol is anything in the world, and that there is no God but one.

Howbeit there is not in all men that knowledge: but some, being used until now to the idol, eat as of a thing sacrificed to an idol; and their conscience being weak is defiled.

For if a man see thee who hast knowledge sitting at meat in an idol's temple, will not his conscience, if he is weak, be emboldened to eat things sacrificed to idols?

What say I then? that a thing sacrificed to idols is anything, or that an idol is anything?