The Concise Oxford Dictionary of World Religions (1454 page)

(Skt.). Sexual intercourse; in Indian religions, particularly
Tantrism
, a vehicle for and metaphor of liberation (
mok
a
).
Although maithuna as a means of liberation is not found in the
Upani
ads
, the cosmic symbolism of the sexual act found there anticipates the
tantras
.
The sexual act as a metaphor of divine union is found in the
Bhakti
tradition, particularly the erotic (
s
g
ra
) bhakti to
K
a
of the Gaudiya
Vai
avas
, in which the bhakta identifies himself with the
gop
s
, especially
R
dh
, and their adulterous love (
par
kiya