Definition of Buddhist Term: Sutra

Buddhas at Wat Arun, Bangkok, Thailand. Leontura, Getty

In Buddhism, the word sutra (Sanskrit for "thread") or sutta (the Pali equivalent) refers to a set of official teachings. Originally the word was used to identify oral teachings thought to have been given directly by the Buddha himself, which was then recited from memory by the Buddha's disciple,  Ananda, at the First Buddhist Council. From Ananda's memory they were collected in the part of the Tripitaka called the Sutra-pitaka.

(For more about how the Tripitaka originated, see "The First Buddhist Scriptures: The Tripitaka or Pali Canon.) It is thought that the Pali Canon was first committed to written form about 400 years after the death of the Buddha. 

For Theravadan Buddhism, these teachings in the Pali Canon that are believed to be from the Buddhas actual spoken words remain the only teachings officially recognized as part of the sutra canon. 

In eastern Buddhism and Tibetan Buddhist, however, it is believed that not only the Buddha, but also respected disciples can, and have, given teachings that are part of the official canon. In those branches of Buddhism, not only are the texts from the Pali Canon accepted, but also other texts that are not traced to the original oral recitations of the Buddha's disciple, Ananda. Even so, these texts are thought to include truth emanating from Buddha-nature and thus are regarded as Sutras.

 For example, the famous Heart Sutra from the Mahayana branch of Buddhism is among the very important Sutras that are acknowledged as not coming from the Buddha himself. 

These later sutras, also regarded as essential texts by many Mahayana schools, are included in what is called the Northern or Mahayana Canon

To confuse matters further, there are some texts that are called sutras but are not. An example of this is the "Platform Sutra," which contains the biography and discourses of the 7th-century Ch'an master Hui Neng. The work is one of the treasures of Ch'an and ​Zen literature. It is generally and cheerfully agreed that the Platform Sutra is not, in fact, a sutra, but it is called a sutra nonetheless.