I’m preaching about idolatry this coming Sunday, including to kids. Having kids in the audience means I have to be really clear. Adults don’t let you away with much; kids even less.
I still think this is the best definition of idolatry I’ve read:
Idolatry is worshiping anything that ought to be used, or using anything that is meant to be worshiped. (Augustine)
According to this definition, we can turn even God into an idol if we try to use him.