In Cardinal Levada’s glossary, charity (or love) is defined as, "The theological virtue by which we love God above all things for his own sake, and our neighbor as ourselves for the love of God." Paul tells us that love is the greatest of the theological virtues: "So faith, hope, love abide, these three; but the greatest of these is love" (1 Cor. 13:13).
Our Sunday Visitor’s Catholic Encyclopedia entry on "Love" defines it as:
[A]ny strong affection, closeness, or devotion to things or persons. The Greeks distinguished four types of love: storge, philia, eros, and agape. Storge, familial love, is a word for the bond that exists between one who loves and persons, animals, and the things that surround him. It is compatible with quite a bit of taken-for-grantedness or even of hatred at times. Philia pertains to friends, freely chosen because of mutual compatibility and common values. Eros is passion, not only of a sexual nature, but also of an aesthetic or spiritual nature, for what is conceived of as supremely beautiful and desirable. Agapic love is manifested when one person has much to give to another more needy. It is generous self-donation without concern for reward.
Such distinctions become especially important in discernments about marriage, because the strength of eros love may blind one to the absence of ther types of love needed to experience a good Christian bond that, with God’s grace, can endure "till death do us part."