A greedy person is someone whose primary goal in life is to get more and more of something they want, and their whole focus is on getting it. We usually think of money when we think of greed, but a person can be greedy for other things also food, fame, possessions, prestige and so forth.
The Bible repeatedly warns us against greed, and we need to take its warnings very seriously especially in our materialistic society. Jesus said, "Watch out! Be on your guard against all kinds of greed; a man's life does not consist in the abundance of his possessions" (Luke 12:15). The Bible also says, "A greedy man stirs up dissension, but he who trusts in the Lord will prosper" (Proverbs 28:25).
What is the problem with greed? The problem first of all is that a greedy person allows things to take the place of God in his life. Instead of putting God and His will first, they put money and things first. Greed is wrong also because a greedy person is concerned only with himself, and overlooks the needs of others. Greed can also lead to other sins, such as jealousy and envy.
Pray for your uncle, that he will realize his need of Christ and put Him first in his life. Even if he isn't greedy in the way I have defined it, money still seems to be more important to him than it should be. Someday the things of this earth will vanish, and the only thing that will matter is our relationship to Christ.