This article is from the Magick Tantra FAQ, by Tyagi Nagasiva firstname.lastname@example.org, Catherine Yronwode email@example.com with numerous contributions by others.
By this is meant very slow, mindful penis-in-vagina
intercourse. Depending on the school of tantra and the
individual preferences of the partners, this may involve
no movement by either party, minimal movement by both
parties, or no movement on the part of the man but some
on the part of the woman. Passive copulation can be
undertaken in any number of positions. One classic is
the Hindu and Tibetan pose in which the woman sits in
the man's lap, commonly known by its Tibetan name,
"yab-yum" (which means "father-mother"). Among those
who practice karezza, more conventional Western sexual
positions such as lying side-by-side or woman-on-top
are preferred for passive copulation because they
require less effort and training. Taoist sexual alchemy
texts advocate the woman-on-top position.