“These forms are known as 'yab-yum' (father-mother) forms. Their union represents the inseparability of relative and absolute, manifestation and voidness, method and wisdom. They also symbolize the union of what are called the 'solar' and 'lunar' energies, the two poles of subtle energy that flow in the subtle energy system of the human body, which is called the 'Inner Mandala'.”

-'The Crystal and the Way of Light: Sutra, Tantra and Dzogchen, Teachings of Chogyal Namkhai Norbu'