Skt., tantra: web, woven together
Tib., rgyud: continuum, transmission, secret teaching
Jap., mikkyo: secret (Buddhist) teachings

A Sanskrit term for a mystical/spiritual and non-dualist system of psychology, philosophy and cosmology which promotes the union of opposites on all levels of being and becoming; from cosmic to quantum levels - on astral, mental and physical planes.

This central theme is expressed in most of its sacred texts, as in its works of art, alchemy, and science. Naturally, the same applies to the ritual observances practiced by Tantrics of both genders.

Women and men are seen as microcosmic expressions and/or mirrors of macrocosmic energies as they are represented by the goddess Shakti and the god Shiva; in whatever guise these may appear. Therefore, in actual practice, the aim is to go beyond all duality and to achieve union.

Sri Yantra

Sri Yantra.
Symbol of Shakti and
Shiva in Union

Tantra, sometimes named Tantrism in Western literature, has influenced and penetrated many other religious schools and therefore comes in several varieties. Apart from the original Indian Tantra and the Tibetan Buddhist Tantra it has brought forth, there's also Chinese, Japanese, and even modern, Western (Neo-)Tantra.
Another, more internal development has led to the distinction between left-handed (Skt., vamacara) and right-handed (Skt., daksinacara) Tantra.

Balanced union of, and between, the opposite poles is thought to be a sure way to achieve liberation of mind and body, a liberation from the supposedly endless cycle of unconscious rebirth.

In order to facilitate such union on all levels of being, Tantra makes use of a variety of physiological, psychological and devotional techniques, many of which have been described or outlined in several of my own books as well as in many other, more specialized works.

In a historical context, Tantra as a system has developed from about the 5th century and reached its peak of social diffusion around the 12th century, but even today it still continues to influence Indian ritual and life.

Originally, Tantra seems to have been a kind of religious and social revolt against foreign invaders, the Aryan, Indo-European peoples, their patriarchal priests and male deities. With its roots in pre-Aryan, Indian spirituality, Tantra re-established once more the tradition of the Great Goddess Shakti and re-infused ancient aboriginal, tribal practices and beliefs into what is generally called Hinduism.

Certain areas, provinces or states of India, in a sense the mother-country of Tantra, have made outstanding contributions to the development of the tradition. Among these, Bengal and Assam are most noteworthy, but also Kerala and Kashmir certainly belong to the Tantric regions.