Yantra is a Sanskrit word means 'an apparatus' .It is a mystic diagram composed of sacred geometric and alphabetic figures and is usually etched on small plates of gold, silver or copper. These are also made in three dimensions in metal crystal and stone.
The purpose of a Yantra. is to focus spiritual and mental energies to invoke a diety or improve health, wealth, progress, prosperity,childbearing and others. It is usually installed near or under the temple Deity. Yantra has also been defined as a visual mantra i.e., it is able to create the vibrations and other mystic effects of a Mantra by sight.
It is a symbol of the entire cosmos that serves to remind the practitioner of the non difference between subject and object.
The most celebrated Yantra in India is the Sri Yantra, the Yantra of Tripura Sundari.