Yab yum

yab yum (ཡབ་ཡུམ།). A Tibetan term that refers to male and female deities in sexual union.

Yab yum literally means father and mother.

StudyBuddhism states:

Just as a father and mother in union are required for producing a child, likewise method and wisdom in union are required for giving birth to enlightenment.

Method, the father, stands for bodhichitta and various other causes taught in tantra for gaining the enlightening physical bodies of a Buddha or a Buddha's omniscient awareness of conventional truth. Wisdom, the mother, stands for the realization of emptiness with various levels of mind, as causes for a Buddha's enlightening mind or a Buddha's omniscient awareness of deepest truth. Gaining the union of a Buddha's physical bodies and mind or a Buddha's omniscient awareness of the conventional and deepest truths of all things requires practicing a union of method and wisdom. Because traditional Indian and Tibetan cultures do not share a Biblical sense of prudishness about sex, they do not have taboos about using sexual imagery to symbolize this union.

The Princeton Dictionary states:

Although interpreted in numerous ways, the male figure is generally understood to represent compassion (karuṇā]) and method (upāya) and the female figure wisdom (prajñā). Their union represents the indivisibility of these two qualities in the state of buddhahood. Although often described in such symbolic terms, numerous sādhanas associated with the anuttarayogatantras include the practice of sexual union.