Yantra

(“instrument”) In astrology (jyotisha),
and in tantra, a secret, ritually based
religious practice, the word yantra
most commonly refers to a symbolic
diagram, often believed to confer
magic or spiritual power on those
who know how to use it. In some cases
such yantras are considered to be an
aniconic form of a deity, as is the case
of the most famous yantra, the
Shriyantra or Shrichakra, which is
used in ritual for the worship of the
goddess Tripura Sundari. The most literal meaning of the word is “device for
restraining,” and in an astrological
setting the yantras of the various
planets are used in rituals to change
their effects, usually to restrain or
diminish the power of planets judged
to be malefic or inauspicious.