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Yuga, in Hindu cosmology, an age of humankind. Each yuga is progressively shorter than the preceding one, corresponding to a decline in the moral and physical state of humanity. Four such yugas (called Sat, Treta, Dvapara, and Kali) make up the mahayuga (“great yuga”), and 2,000 mahayugas make up the basic cosmic cycle, the kalpa. The first yuga (Sat) was an age of perfection lasting 1,728,000 years. The fourth and most-degenerate yuga (Kali) is the present age, which began in 3102 BCE and will last 432,000 years. At the close of the Kali yuga, the world will be destroyed, to be re-created after a period of quiescence as the cycle resumes again.

 In Hindu astronomy, a yuga is a unit of time consisting of five solar years.

As per Nilesh Nilkanth Oak, there are 30 different numbers of years assigned for each yuga which varies from 4 yugas in one year to 3,024,000 years in 4 yugas.