In Hindu culture, the term gotra (Sanskrit: गोत्र) is broadly considered equivalent to lineage. It refers to people who are descendants in an unbroken male line from a common male ancestor, that is, a patriline. The concept is woven into traditional notions of family identity and descent across many Hindu communities.
The gotra generally functions as an exogamous unit. By customary practice, marriage within the same gotra is regarded as incestuous and is therefore prohibited. For this reason, knowledge of one's gotra is considered important in arranging marriages, especially within caste-based traditions among Hindus.
While the name of a gotra can sometimes be used as a surname, the gotra itself is distinct from a surname. It is maintained with care because of the role it plays in matrimonial customs, and it is often cited separately from family names during ritual and ceremonial occasions.
The grammarian Pāṇini provides a classical definition in his sūtra apatyam pautraprabhṛti gotram (IV.1.162). Following the explanation derived from the Monier Williams Dictionary, this indicates that the word gotra denotes the descendants (apatya) of a couple consisting of a pautra, a son, and a bhartrī, a mother or daughter-in-law. The definition thus places the gotra within a framework of generational descent traced through male progeny.
Adapted from the English Wikipedia article on Gotra.