Buddha’s teaching were transmitted orally from one generation to the next, as was the custom in India, and centuries later gathered together and written down to form ‘The Three Baskets’ (Tripitaka) or collections of Buddhist teaching:
Sutras – The collection of Buddha’s oral teachings.
Vinaya – The rules of ethical behavior for monks, nuns and lay people.
Abhidharma – Philosophical teachings on the true nature of phenomena.
In addition, there is the collection of esoteric Buddhist teachings given by the Buddha in the tantras.
Subsequently, the great Indian and Tibetan Buddhist masters composed explanatory teachings that summarize and elaborate on specific topics to help students study and practice. These are known as ‘shastras’.