From Nagarjuna's Treatise on the Great Perfection of Wisdom
Then again, dana is of three varieties: The first is the giving of material objects. The second is giving which consists of offerings of reverence. The third is the giving of Dharma.
What is meant by the giving of material objects? It refers to jewels, precious things, robes, food, one's head, eyes, marrow and brain. One gives exhaustively of such things as these, giving all that one owns whether internally or externally. This is what is meant by the giving of material objects.
As for the giving of reverence, it refers to having a mind of faith which is pure as one reverently performs acts of obeisance. It refers to offerings which consist of looking after, seeing off, welcoming, making expressions of praise, and circumambulating. All sorts of actions such as these constitute what is referred to as the giving of reverence.
As for the giving of Dharma, [it refers to actions performed] for the sake of virtue associated with the Way such as speaking, dialectical discussion, reciting, reading, lecturing, dispelling doubts, answering questions, transmitting the five precepts to people and all sorts of other acts of giving such as these which are performed for the sake of the buddha way. This is what is meant by the giving of Dharma. When these three kinds of giving are fulfilled this is what is meant by fulfilling dana paramita.