Original: These are the Krita Yuga, the Treta Yuga, the Dvapara Yuga, and finally the Kali Yuga.
Simplified: Hindus believe that there are periods of time called yugas ("ages" or "eras"): Satya Yuga, Treta Yuga, Dvapara Yuga, and Kali Yuga. When Kali Yuga ends, a new Satya Yuga begins.