in Hinduism, a brief, aphoristic composition; in Buddhism, a more extended exposition, the basic form of the scriptures of both the Theravāda (Way of Elders) and Mahāyāna (Greater Vehicle) traditions. The early Indian philosophers did not work with written texts and later often disdained the use of them; thus, there was a need for explanatory works of the utmost brevity that could be committed to memory. The earliest sūtras were expositions of ritual procedures, but their use spread. Pāṇini's grammatical sūtras (5th–6th century BC) became in many respects a model for later compositions. All the Indian philosophical systems (except the Sāṃkhya, which had its kārikās, or doctrinal verses) had their own sūtras, most of which were preserved in writing early in the Christian Era.

Different from its usages in Hindu literature, the Buddhist sūtra denotes a doctrinal work, sometimes of considerable length, in which a particular point of doctrine is propounded and deliberated. The most important collection of the Theravāda sūtras is to be found in the Sutta section of the Pāli canon, which contains the discourses attributed to the Gautama Buddha. In Mahāyāna Buddhism the name sūtra is applied to expository texts.