Tuft of hair on head in Hinduism is known as Shikha. Males keep a tuft of hair at the rear end of their head. In religious parlance, it also refers to the hair grown in four other parts, namely, the two eyebrows, and on the two arms between the wrist and elbow. These five parts of body, with hair growing on them go by the name of panchasikha. The name is jrsikha if the last mentioned (the two arms between the wrist and elbow) are eliminated.
In ancient India, every male used to maintain the tuft as a custom. Subsequently, with the admixture of culture and civilization, only priestly class used to maintain it, since its possession was imperative while worshiping in the temple or in the house. Every Hindu is expected to have the tonsure, and there is a prescription that the tuft must be of the size and shape of cow’s hoof. Even when hair is to removed from all over the body, the tuft will remain.
It is also held that the tuft of hair formed a protective centripetal element guarding the nerve center at the rear of a man’s head. It was also believed that it was a sure guard against witchcraft.
Bodhayana Grihya Sutra records how maintenance of sikha makes one qualified to perform Vedic rituals and recommends (ekasikha) tuft and jrsikha (eye brows) and panchasikha (all the five regions enumerated) as is prescribed in the code of conduct.
It is usual to place the wrist with the thumb pointed straight while depositing sikhayaivasata (an oblation) over the tuft either at the rear or at the front, depending upon kuladharma (practice of the clan), since it is shaktipitha (source of energy) in the body.
Notes taken from Encyclopedia of Hinduism Volume IX page 455 - IHRF