The term vajra is a Sanskrit word that is usually defined as diamond or thunderbolt. It also defines a kind of battle club that achieved its name through its reputation for hardness and invincibility. The vajra has special significance in Tibetan Buddhism, and the word is adopted as a label for the Vajrayana branch of Buddhism, one of the three major forms of Buddhism. The visual icon of the vajra club, along with the bell (ghanta), form a principal symbol of the Vajrayana Buddhism of Tibet.