Yantra literally means "instrument". A Yantra is a geometric design acting as a highly efficient tool for contemplation, concentration and meditation. Yantras carry spiritual significance, and point the user to higher levels of consciousness.
The Yantra provides a focal point that is a window into the absolute. When the mind is concentrated on a single, simple object (in this case a Yantra), the mental chatter ceases. Eventually, the object is dropped when the mind can remain empty and silent without help. In the most advanced phases, it is possible to attain union with God by the geometric visualization of a Yantra.