Tantra was a religious sect in ancient India. What made Tantra different from other religious groups is that the tantrikas, the followers of Tantra, believed that personal fulfillment & union with God, came through living, accepting, & gaining a deep understanding of all of life’s energies and experiences & taught that there’s nothing in life that one needs to turn away from to be spiritual or holy.
To this day there are temples in India that have on their exterior walls sculpted images of couples in various sexual acts. Those are the remnants of Tantra. The religion as such has become nearly invisible in the public eye and today in the west it is often misunderstood.