PārājikakaṇḍaPaṭhamapārājikasikkhāpada

Vinayapiṭaka · Bhikkhu Vibhaṅga (1) · Vol. 1 · Section 33

[33] "Sexual intercourse (methunadhamma)" means: that act which is the practice of the ignoble (asaddhamma), the practice of villagers (gāmadhamma), the practice of the low-born (vasaladhamma), coarse, ending with water, done in secret, the coming together of a couple, two by two — this is called sexual intercourse.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.