In Hindu society, the term gotra means clan. It broadly refers to people who are descendants in an unbroken male line from a common male ancestor or patriline. Gotra can be used as surname but it is different from surname and is strictly maintained because of its importance in marriages among Hindus and especially among the high Hindu-castes. Pāṇini defines gotra for grammatical purposes as apatyam pautraprabhrti gotram (IV. 1. 162), which means "the word gotra denotes the progeny (of a sage) beginning with the son's son." When a person says "I am Kashyapa-gotra," he means that he traces his descent from the ancient sage Kashyapa by unbroken male descent. According to the Brihadaranyaka Upanisad 2.2.6, Gautama and Bharadvāja, Viśvāmitra and Jamadagni, Vashishtha and Kaśhyapa, and Atri are seven sages (also known as Saptarishi); the progeny of these eight sages is declared to be gotras. This enumeration of eight primary gotras seems to have been known to Pāṇini. The offspring (apatya) of these eight are gotras and others than these are called gotrâvayava. There exists another theory about gotra: sons of rishi and disciples of the gurukul would have the same gotra. It is believed that they possess similar thoughts and philosophies. People of the same gotra can be found in different castes.
As a Rigvedic term, gotra simply means "cow shelter" or "herd of cows". The narrowed meaning "family, lineage kin" (as it were "herd within an enclosure") is younger, first recorded around the mid 1st millennium BCE (e.g., Chandogya Upanishad).
These "lineages" as they developed among the Brahmins of that time meant patrilineal descent. The Brahmanic system was later adopted by other communities, such as the Kshatriyas and Vaisyas
All members of a particular gotra are believed to possess certain common characteristics by way of nature or profession. Many theories have been propounded to explain this system.
According to the brahminical theory, the Brahmins are the direct descendants of seven or eight sages who are believed to be the mind-born sons of Brahma. They are Gautama, Bharadwaja, Vishvamitra, Jamadagni, Vashista, Kashyapa, and Atri. To this list, Agasthya is also sometimes added. These eight sages are called gotrakarins from whom all the 49 gotras (especially of the Brahmins) have evolved. For instance, from Atri sprang the Atreya and Gavisthiras gotras.
A gotra must be distinguished from a kula. A kula is a set of people following similar cultural rituals, often worshiping the same divinity (the Kula-Devata, god of the clan). Kula does not relate to lineage or caste. In fact, it is possible to change one's kula, based on one's faith or Iṣṭa-devatā.
These eight rishis, called Gotrakarins created all the 49 Gotras. The members of a Gotra may not be blood relations but can be the spiritual inheritors or descendants of a Guru or his followers.
The members of a particular Gotra are believed to possess certain common characteristics by way of nature, skills, and profession.
In ancient times the members of the brahminical Gotras had certain characteristic features to distinguish from the others.like- the Bhargavas used to shave their heads, while the Angirasas had five braids.
As the time elapsed, the number of Gotras increased due to following reasons-
a) The Descendants of original rishi gave rise to a new family lineage ie new Gotras,
b) By intermarriage with other sub-groups of the same caste,
c) Following a new rishi and adopting his Gotra.
A common mistake is to consider gotra to be synonymous with cult or Kula. A kula is basically a set of people following similar rituals, often worshipping the same God (the Kula-Devata - the God of the cult). Kula has nothing to do with lineage or caste. In fact, it is possible to change one's Kula, based on his faith or ista devata.
It is common practice in Hindu marriage to enquire about the Kula-Gotra meaning Cult-Clan of the bride and bridegroom before approving the marriage. In almost all Hindu families, marriages within the same gotra are prohibited. But marriage within the kula is allowed and even preferred.
The word "Gotra" means "lineage" in the Sanskrit gotra, as given names may reflect the traditional occupation, place of residence, or another important family characteristic rather than gotra. Language. While it is somewhat akin to a family name, the given name of a family is often different from its gotra, as given names may reflect the traditional occupation, place of residence, or other important family characteristics rather than gotra.
People belonging to the same gotra also belong to the same caste in the Hindu social system.
Many lines of descent from the major rishis were later grouped separately. Accordingly, the major gotras were divided into ganas(subdivisions) and each gana was further divided into groups of families. The term gotra was then frequently started being applied to the ganas and to the sub-ganas.
Every brahmin claims to be a direct patrilinial descendant of one of the founding rishis of a certain gana or sub-gana. It is the gana or sub-gana that is now commonly referred to as gotra.