medium kalpa ［中劫］ ( chū-kō): A unit of time in ancient Indian cosmology. Medium kalpa can refer to either of two different periods of time. One is any of the twenty kalpas that constitute each of the four kalpas of formation, continuance, decline, and disintegration. (According to one account, a medium kalpa is 15,998,000 years.) The other is a total of those twenty kalpas or the period of any of the four kalpas mentioned above.