three uncountable kalpas (Sanskrit, try-asaṃkhyeya-kalpa). The period of time necessary for a Bodhisattva to arrive at enlightenment (bodhi), according to the Mahāyāna. The precise duration of one ‘uncountable’ (asaṃkhyeya) kalpa or aeon varies but values sometimes given are 1051, 1059, or 1063 years. Other sources describe these in terms of spans of time of inconceivable duration.

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