Yantras are the geometrical form of a divinity in the tantrik tradition. Yantras can be drawn, engraved or painted on a variety of substances. The yantra shown left is for Kali , and can be used to illustrate the basic geometrical concepts used. The point or bindu at the centre, generally represents the deity, or sometimes Shiva and Shakti united. The triangle normally represents the three gunas, or in the case of the tantrik tradition, the three bindus.
Triangles usually face downwards in the case of female yantras and upwards in male yantras.
There are exceptions - the Shri Yantra is one such. Triangles are often surrounded by enclosing circles and a group or groups of petals, in which are the attendants of the Devis or Devas. See the Mahamrityunja yantra for a complete example. Finally, the whole is often enclosed in a bhupura, a word which means earth-city. Some traditions use the yantra in puja from the outside inward, and others from the inside outward, depending on the nature of the deity.