The whole teaching of the Buddha, in terms of Buddhism, can also be called Dhamma, Sasana, or Desana. The term, "Dhamma", is a Pali word which means to bear or to hold up or support. That is, the Dhamma holds up or supports one who lives up to its principles so that one will not suffer in lower miserable abodes (apaya). The Dhamma in its full sense means truth, that which really is. It also means Law, the law which exists in mans mind body and in the universe. It consists of the natural principles of its own cosmic order.
The Dhamma has been founded on the original conditions of man and the universe and therefore man and the universe are only the states or the conditions of the Dhamma. Just as the Dhamma, the natural Law exists in the universe, it also positively exists in the mans mind and body. The Dhamma actually means natural principles of righteous path for a man to liberate himself from the miseries of life and to reach the state of supreme peace and happiness — Nibbana. The Buddha Himself had found out the very state of ultimate liberation and revealed it to others with His enlightened wisdom, i.e., He taught to all mankind the Dhamma — the only straight path that leads thereto.
Nevertheless, Buddhism is not the kind of revelation created by any Supernatural Being or God, but natural or universal principles discovered through a practical experience by a holy human being, the enlightened Buddha. The principles in the Teaching are something like guidance for one who has mistaken a wrong way, or like the medicine for a patient who is seriously sick from diseases of defilements, or like a map for a traveller who is ignorant of the way to take for his journey. The Dhamma indeed consists of ways and means on how one is to live for ones mental or spiritual evolution of life towards the climax of ever lasting peace and happiness.
The other two terms — "Sasana" and "Desana" - have also the same connotations. Sasana is a Pali word which means advice or exhortation or injunction of the Buddha. There are three kinds of Sasana, namely, 1. study or theoretical aspect of the Dhamma (pariyatti,), 2. practice or practical aspect (patipatti,), and 3. attainment of enlightenment in Nibbana by way of the Path (magga) and Fruition (panna), i.e. realizable aspect (pativedha). Desana is also a Pali term too, which consists of all the words or teachings delivered by the Buddha Himself during His life time.