Tantra is a broad current of ritual, yogic and esoteric practice that arose within Hinduism and Buddhism in the middle of the first millennium and reshaped both. The name refers in the first place to a class of scriptures, the Tantras, and the traditions built on them are better described as a distinctive style of practice than as a single doctrine. Characteristic features include the use of mantra (sacred sound), yantra and mandala (sacred diagram), the visualisation and internalisation of deities, the mapping of a subtle physiology of channels and centres within the body, and an initiatory transmission from master to disciple that is essential and non-negotiable. Tantra typically holds that the same energies that bind a person in the world can, rightly harnessed, liberate them, and so it turns toward what orthodox practice shuns rather than away from it.
This is the point at which popular Western usage most badly distorts the subject. In its home traditions tantra is overwhelmingly a matter of ritual, mantra, visualisation and yogic discipline within a demanding ascetic and devotional frame; the sexualised "tantra" marketed in the modern West is a twentieth-century construction only loosely connected to the historical traditions.