In Hindu culture, the term gotra is considered to be equivalent to lineage. It broadly refers to people who are descendants in an unbroken male line from a common male ancestor or patriline. Generally, the gotra forms an exogamous unit, with marriage within the same gotra being regarded as incest and prohibited by custom. The name of the gotra can be used as a surname, but it is different from a surname and is strictly maintained because of its importance in marriages among Hindus, especially among castes. Pāṇini defines gotra as apatyam pautraprabhrti gotram, which means "the word gotra denotes the descendance, apatya, of a couple consisting of a pautra, a son and a bharti, a mother, i.e. a daughter-in-law."