What is Tantra?

A simple question without a simple answer, and any attempt at definition will necessarily be incomplete. The roots of the word are Sanskrit:

Through Tantric practice one can experience an expansion of consciousness and recognize the interconnectedness of the web of existence.

At the same time, Tantra can refer to any of a number of sacred texts in the Hindu, Jain and Tibetan Buddhist traditions. Many of these texts contain detailed guidelines for spiritual practice. From this perspective, Tantra is a vast body of spiritual and physical knowledge, encompassing an array of practices, including all forms of yoga. These practices are aimed at expan- ding consciousness and liberating oneself "through life and not through escape, using  the body as an instrument." 

In Tantra, the energies of the body are used as the fuel for spiritual develop- ment.

In the West, Tantra is often called the "Yoga of Sex." While there is a kernel of truth in this phrase, the popular press has created a misleading impression that Tantra is about having better orgasms or about becoming a better lover. Since Tantric practices are designed to expand consciousness, they can expand a person's capacity to give, receive and experience pleasure, not only in the sexual realm but in all areas of life, provided that person is willing
to do the work.

Many Western Tantra teachers emphasize very powerful techniques for enhancing sexual pleasure and intimacy, while some traditional teachers discourage students from exploring sexual Tantra at all. 

from Ecstasy Through Tantra by Dr. Jonn Mumford