In Sanskrit: वज्र, Tibetan: Dorje རྡོ་རྗེ “thunderbolt, lightning, diamond, adamantine”. In Hinduism, the weapon of Indra. In Tibetan Buddhism, a symbol of true reality, the Emptiness, the Absolute, that which is indestructible.
The tip of the vajra [phallus] is placed firmly in the lotus [vagina]
And mind as the syllable HUM is brought into the central channel [of the spine]; Dalai Lama: Innate Joy.