om krim krim krim hum hum hrim hrim svaha
Hindu Tantra is the "black magick" of India. While in the West its mostly associated with sex, its practices involve engaging one's taboos as a way to free up energy. In one of its more famous practices, Panchamakara (or "five M's"), tantrikas ritually engage in the five traditional taboos of Hinduism: meat (mamsa), wine (madya), fish (matsya), ritual gesture (mudra), and sex (maithuna).
Tantric Buddhism is a bit of a different creature. Some of the same goddesses are involved (for example,Tara) and there are certainly similarities in the ritual approaches (i.e. heavy visualization, often horrific). What distinguishes Tantric Buddhism from Hindu is its emphasis on Boddhichitta, compassion.
Its Hindu Tantra that I know the most about, and I hope to fill in this space with more info on that in the near future.