Yuga
A yuga, in Hinduism, is generally used to indicate an age of time.
In the Rigveda, a yuga refers to generations, a period of time, or a yoke. In the Mahabharata, the words yuga and kalpa are used interchangeably to describe the cycle of creation and destruction.
In post-Vedic texts, the words "yuga" and "age" commonly denote a Yuga Cycle|, a cycle of four world ages—for example, in the Surya Siddhanta and Bhagavad Gita —unless expressly limited by the name of one of its minor ages: Krita Yuga, Treta Yuga, Dvapara Yuga, or Kali Yuga.
The term "yuga" can represent the number 4. In early Indian astronomy, it referred to a five-year cycle starting with the conjunction of the sun and moon in the autumnal equinox.