'Idol' in the Bible

As to eating things which have been sacrificed to idols, we are fully aware that an idol is nothing in the world, and that there is no God but One.

But all believers do not recognize these facts. Some, from force of habit in relation to the idol, even now eat idol sacrifices as such, and their consciences, being but weak, are polluted.

Do I mean that a thing sacrificed to an idol is what it claims to be, or that an idol is a real thing?