Charity is the Catholic term for love. It means "to will the good of another as one's own."
Charity is 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. - CCC 1822
Here's what the Catechism has to say about Charity:
Jesus makes charity the new commandment. By loving his own "to the end," he makes manifest the Father's love which he receives. By loving one another, the disciples imitate the love of Jesus which they themselves receive. Whence Jesus says: "As the Father has loved me, so have I loved you; abide in my love." and again: "This is my commandment, that you love one another as I have loved you."
Fruit of the Spirit and fullness of the Law, charity keeps the commandments of God and his Christ: "Abide in my love. If you keep my commandments, you will abide in my love."
Christ died out of love for us, while we were still "enemies." The Lord asks us to love as he does, even our enemies, to make ourselves the neighbor of those farthest away, and to love children and the poor as Christ himself.
The Apostle Paul has given an incomparable depiction of charity: "charity is patient and kind, charity is not jealous or boastful; it is not arrogant or rude. Charity does not insist on its own way; it is not irritable or resentful; it does not rejoice at wrong, but rejoices in the right. Charity bears all things, believes all things, hopes all things, endures all things."
"If I . . . have not charity," says the Apostle, "I am nothing." Whatever my privilege, service, or even virtue, "if I . . . have not charity, I gain nothing." Charity is superior to all the virtues. It is the first of the theological virtues: "So faith, hope, charity abide, these three. But the greatest of these is charity."
The practice of all the virtues is animated and inspired by charity, which "binds everything together in perfect harmony"; it is the form of the virtues; it articulates and orders them among themselves; it is the source and the goal of their Christian practice. Charity upholds and purifies our human ability to love, and raises it to the supernatural perfection of divine love.
The practice of the moral life animated by charity gives to the Christian the spiritual freedom of the children of God. He no longer stands before God as a slave, in servile fear, or as a mercenary looking for wages, but as a son responding to the love of him who "first loved us":
If we turn away from evil out of fear of punishment, we are in the position of slaves. If we pursue the enticement of wages, . . . we resemble mercenaries. Finally if we obey for the sake of the good itself and out of love for him who commands . . . we are in the position of children.
The fruits of charity are joy, peace, and mercy; charity demands beneficence and fraternal correction; it is benevolence; it fosters reciprocity and remains disinterested and generous; it is friendship and communion:
Love is itself the fulfillment of all our works. There is the goal; that is why we run: we run toward it, and once we reach it, in it we shall find rest.