YANTRA literally means "support" and "instrument". A YANTRA is a geometric design that serves as a highly efficient tool for contemplation, concentration and meditation. YANTRAS has a spiritual meaning: there is a specific meaning that relates to higher levels of consciousness.
The YANTRA offers a focus that is a window into the absolute. When the mind is focused on a single, simple object (in this case a YANTRA) the mental chatter stops. Eventually the object will be dropped when the mind can remain empty and still unaided. In the most advanced phases it is possible to achieve union with God through the geometric visualization of a YANTRA.
The YANTRA is like a microcosmic image of the MACROCOSM. It is a focus point and an outside and inside door. The YANTRAS often focus on a particular deity and such. By attuning to the different YANTRAS, you can tap into certain deities or creative centers of power in the universe.
YANTRAS are usually designed so that the eye is centered, and very often they are symmetrical. They can be drawn or three-dimensional on paper, wood, metal or earth.
The most famous YANTRA in India is the Sri YANTRA, the YANTRA of Tripura Sundari. It is a symbol of the entire cosmos that reminds the practitioner of the nondifference between subject and object.