The most subtle of all the commandments. It is the most difficult to define and to distinguish. To covet is not simply to want something. God has give us appetites, drives, and desires. These are given to us for our good, the good of others and the glory of God, if used and disciplined under the power of the Spirit of God.
Covetousness is more than desire.
To covet is not just to admire something someone else has. We should rejoice in the good fortune of others. To covet is to desire as my own what another has and to which I have no right or claim. To covet is to allow a desire for anything to take control of my heart. Remember, an idol is that this displaces God or misrepresents God.