Idolatry covers a lot of ground and infringes upon a lot of modern day practices. You first have the more obvious type of idolatry which is worshipping false gods; this was particularly common during the Biblical days when groups all over the world would create gods and carve them out of wood in anything from little tiny palm-sized statues to the large effigies that we see elsewhere made of stone.Isaiah 37:19And have cast their gods into the fire: for they were no gods, but the work of men's hands, wood and stone: therefore they have destroyed them.Idolatry also covers the concept of making an image of God or worshipping something or someone in his place. We see this being practiced all throughout history and unto this very day. You had many of the sun worshippers of old who worshipped the sun and then there were also star worshipers though they sometimes claimed or even thought that they were worshipping god.2 Kings 17:16And they left all the commandments of the LORD their God, and made them molten images, even two calves, and made a grove, and worshipped all the host of heaven, and served Baal.2 Kings 21:3For he built up again the high places which Hezekiah his father had destroyed; and he reared up altars for Baal, and made a grove, as did Ahab king of Israel; and worshipped all the host of heaven, and served them.2 Kings 23:5And he put down the idolatrous priests, whom the kings of Judah had ordained to burn incense in the high places in the cities of Judah, and in the places round about Jerusalem; them also that burned incense unto Baal, to the sun, and to the moon, and to the planets, and to all the host of heaven.Now we have many modern day cults where people worship to images of Christ on the cross or images of saints passed many generations ago. All of this falls under the idol worship that the Bible warned about. When you start worshipping a material thing, you lose sight of God.I've even heard this applied to people who "worship" material aspects of wealth and so forth. I think this is accurate and falls under idol worship in many cases.