In Hindu religion, Dharma Shastras are social laws that include the codes of conduct to be observed by individuals living in a society. Dharma Shastras are works by various sages of ancient India 
A particular Dharma Shastra is applicable only during a Manvantara. A manvantara is the period of time or duration that a Manu (the archetypal human being) rules the entire creation. One Manvantara is 306,720,000 human years.
Apart from Manu, the other Dharma Shastras that are applicable in different periods are named after Apastamba, Bharadvaja, Daksha, Devala, Samakha, Vasishta, Gautama, Samavarata, Vishnu, Harita, Shatanika, Vyasa, Likhita, Shatotraya, Yajnavalkya, Parashara, Sahunaka and Yama.
(Reference: Hinduism Frequently Asked Questions by Chinmaya Mission)
