Overview
A yantra (Sanskrit: यन्त्र, yantrá, literally 'machine' or 'contraption') is a geometrical diagram associated mainly with the Tantric traditions of the Indian religions. Yantras are used in the worship of deities in temples and homes, as aids in meditation, and for benefits believed to arise from their occult properties as described in Hindu astrology and tantric texts. They are also employed in the adornment of temple floors, owing to their aesthetic and symmetric qualities.
Specific yantras are traditionally associated with particular deities or with certain types of energies, and are used in the accomplishment of tasks or vows of either a materialistic or spiritual nature. They serve as a prime tool in certain sadhanas undertaken by the sadhaka, or spiritual seeker. Yantras hold significance in Hinduism, Jainism, and Buddhism.
Representations resembling the yantra in India have been considered to date back to a remote antiquity. The Baghor stone, found in an Upper Paleolithic context in the Son River Valley, has been described by G. R. Sharma, who was involved in its excavation, as among the earliest such examples. The triangular stone, bearing triangular engravings on one side and daubed in ochre, was found at a site associated with worship. Goddess worship in that region was observed to be practised in a manner similar to present-day traditions. Kenoyer, who was also part of the excavation, associated the find with Shakti. The triangular form has been compared to the Kali Yantra and the Muladhara Chakra.
Mantras, the Sanskrit syllables inscribed on yantras, are described in tradition as "thought forms" representing divinities or cosmic powers, believed to exert their influence by means of sound-vibrations. The combination of geometric form and inscribed syllable thus links visual and acoustic elements within ritual and meditative practice.
References
Adapted from the English Wikipedia article on Yantra.