sexual intercourse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Sexual union between a male and a female involving insertion of the penis into the vagina.
• noun Sexual activity that includes insertion of the penis into the anus or mouth.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Sexual interaction, usually involving genital and/or anal and/or oral penetration, between at least two organisms.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the act of sexual procreation between a man and a woman; the man's penis is inserted into the woman's vagina and excited until orgasm and ejaculation occur