Maithuna
Maithuna (Devanagari: मैथुन) is a Sanskrit term used in Tantra most often translated as "sexual union" in a ritual context. It is the most important of the five makara and constitutes the main part of the Grand Ritual of Tantra variously known as Panchamakara, Panchatattva, and Tattva Chakra. 

Although some writers, sects and schools, e.g. Yogananda, consider this to be a purely mental and symbolic act, a look at different variations (and translations) of the word maithuna clearly shows that it refers to male-female couples and their union in the physical, sexual sense and is synonymous with kriya nishpatti (mature cleansing). Just as neither spirit nor matter by itself is effective but both working together bring harmony so is maithuna effective only then when the union is consecrated. The couple become for the time being divine: she is Shakti and he is Shiva, and they confront ultimate reality and experiences bliss through union. The scriptures warn that unless this spiritual transformation occurs the union is incomplete.

Yet it is possible to experience a form of maithuna not solely just through the physical union. The act can exist on a metaphysical plane with sexual energy penetration, in which the shakti and shakta transfer energy through their subtle bodies as well. It is when this transfer of energy occurs that the couple, incarnated as goddess and god via diminished egos, confronts ultimate reality and experiences bliss through sexual union of the subtle bodies.

Main significations
 Paired polarity
 Couple
 Loving couple
 The amorously entwined couples featured on Indian high-reliefs and statues found in temples such as Khajuraho and Konark Sun Temple.
 The zodiac sign of Gemini, which in India is not a figure of twins as in the West, but that of a man and woman representing Maithuna, derived from the Sanskrit word 'Mithuna', a couple.

Other spellings
mithunam: Sexual union, copulation, intercourse (Sanskrit)
Maithunam dravyam: the unrefined fluid from intercourse (D.G. White, p. 84)

Notes