Shastra (from shas, to order or enjoin) is a term for any authoritative scripture in the Brahminical or Hindu tradition. For example, the ARTHASHAS-TRA is an authoritative scripture on artha (worldly action) as it relates to a king. The DHARMASHAS-TRA is authoritative scripture concerning DHARMA (right conduct).
Further reading: A. L. Basham, The Wonder That Was India (Calcutta: Rupa, 1997); Klaus K. Klostermaier, A Survey of Hinduism (Albany: State University of New York Press, 1989).
Encyclopedia of Hinduism. A. Jones and James D. Ryan. 2007.