SHRUTI (Sruti), Skt., lit. “hearing”; the holy scriptures of Hinduism are divided into shruti and smriti. Shruti includes all those texts that derive from divine revelation and hence hold absolute authority. These are the Vedas, whose eternal, sacred sound was “heard” by the rishis. However, of these texts only the Samhitās, Brāhmanas, Upanishads, and certain Sūtras are designated as shruti.
Source: The Encyclopedia of Eastern Philosophy and Religion: Buddhism, Hinduism, Taoism, Zen. Shambhala Publications, Inc.
Documents on the Shruti
Books on Shruti