cakra 

(Sanskrit; Pāli, cakka). 1. A wheel, often used symbolically in Buddhism to signify the various aspects of the Dharma. With eight spokes it connotes the Eightfold Path, and with twelve spokes the doctrine of Dependent Origination (pratītya-samutpāda) or three turnings of the wheel (three times the Four Noble Truths as mentioned in the first sermon).

2. In anuttara-yoga-tantric practice, the cakras are energy centres in the body, located along the subtle channels (nāḍī); different numbers of cakras are described according to the specific meditational systems, ranging from three to five or six. It should be noted that the names and descriptions of these energy centres do not correspond to those found in Hindu tantra, and there is no standard set of names and descriptions for the cakras in either Hinduism or Buddhism (standardized versions are all modern inventions).

3. A religious diagram, or maṇḍala.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)