Basically don't allow any kind of greed in heart nor in thought. Don't desire anything that's not yours.
It is a desire to possess something belonging to another.
It particularly applies to wanting the possessions of others.
Covet means to strongly desire that which belongs to another.
Coveting which the Tenth Commandment condemns is the desire to have something which one does not have, or which one does not think he or she has enough of.
When a desire surpasses trusting God for an object it is coveting.
It means, to desire anything not yours.
It means to desire with lust something of someone elses.
These are good definitions for what "covet" means in Ex 20:17; Rom 7:7; Rom 13:9; etc. But it's not what covetousness means in general. Thus these definitions are misleading in deciding everyday life situations. In the LXX & NT the verb translated "covet" is "epithymeo." The noun "covetousness" is "epithymia."
Basically, "covetousness" is a strong desire and thus occasionally translated as "longing." Both the verb and noun are used many times in the NT, frequently in a positive sense. So, desire is not always bad and one must distinguish between bad desires and good desires:
Mat 13:17 For truly I say to you that many prophets and righteous men have desired to see those things which you see, and have not seen them, and to hear those things which you hear, and have not heard them.
Luke 15:16 He desired to eat the carob pods the pigs were eating, but no one gave him anything.
Luke 16:21 Lazarus longed to eat the crumbs that fell from the rich man’s table. Instead, dogs would come and lick his sores.
Luke 17:22 Then he said to the disciples, “The days are coming when you will desire to see one of the days of the Son of Man, and you will not see it.
Luke 22:15 And he said to them, “I have eagerly desired to eat this Passover with you before I suffer.
Gal 5:17 For the flesh has desires that are opposed to the Spirit, and the Spirit has desires that are opposed to the flesh, for these are in opposition to each other, so that you cannot do what you want.
Phi 1:23 I feel torn between the two, because I have a desire to depart and be with Christ, which is better by far,
1Th 2:17 But when we were separated from you, brothers and sisters, for a short time (in presence, not in affection) we became all the more fervent in our great desire to see you in person.
1Ti 3:1 This saying is trustworthy: “If someone desires to the office of overseer, he desires a good work.”
Heb 6:11 Our great desire is that you will keep on loving others as long as life lasts, in order to make certain that what you hope for will come true.
1Pe 1:12 It was revealed to them that in their search they were not serving themselves but you. These things, which even angels desire to examine, have now been proclaimed to you by those who brought you the good news. They did this in the power of the Holy Spirit, who was sent from heaven.
