The worship of idols, images, or anything
made by hands, or which is not God.

"Idolatry is of two kinds; the worship of images, statues, pictures, etc., made by hands; and the worship of the heavenly bodies, the sun, moon, and stars, or of demons, men, and animals." 
Webster's 1828

Also, excessive attachment or
veneration for anything,
or that which borders
on adoration
or worship.
...Mortify therefore your members which are upon the earth; fornication, uncleanness, inordinate affection, evil concupiscence, and convetousness, which is idolatry...

Colossians 3:5