Janeu, also known as the sacred thread or the Yajnopavita, is a consecrated thread worn by certain Hindu men during religious ceremonies, particularly those belonging to the Brahmin, Kshatriya, and Vaishya castes. It is considered a symbol of the initiation into the sacred knowledge and responsibilities of an individual's caste and their connection to the divine.

The janeu is typically made of cotton or silk and consists of three strands that are intricately twisted together. It is usually worn diagonally across the left shoulder and hangs down the right side of the body, passing under the right arm. The thread is generally looped around the ear to prevent it from slipping off.

The wearing of the janeu is associated with the Upanayana or the initiation ceremony, which marks the transition of a young boy into adulthood and the start of his formal education in Vedic scriptures. During the ceremony, the guru (spiritual teacher) performs rituals and imparts sacred mantras to the boy, symbolizing his entry into the world of knowledge and spirituality.

The janeu represents the sacred connection between the individual and the divine. It is believed to provide protection, spiritual guidance, and the ability to perform religious rituals and responsibilities. It serves as a constant reminder of one's duties and obligations towards society, ancestors, and deities.

While the janeu is traditionally associated with men, there are also variations and practices among different Hindu communities. Some communities have different forms of sacred threads for women or may have alternative rituals and practices that signify initiation and spiritual connection.

It's important to note that the significance and practices related to the janeu may vary among different regions, castes, and traditions within Hinduism.