There are dozens of names for it (banging, bonking, fornicating, f**king, getting laid, riding, screwing, shagging...) but sexual intercourse is penetrative sex. (...) Here's how vaginal sex works between a man and a woman. (...) Remember - nobody has the right to make you do more than you want to when it comes to sexual activity. It may take weeks, months or years for two people to both feel ready for sex, and it's important you BOTH feel ready.
Sexual intercourse is the a sexual act that takes place between a Human Male and Female. In Animals the corresponding act is called mating. It can involve animals of the same (or closely related) species. It Mammals including humans, it involves the male placing his Penis inside the Vagina of the female and moving it in and out until he ejaculates. Upon ejaculation (if no Condom or other Contraception is used), the sperm travels to the egg (if the female is ovulating), if it is fertilized the zygote now makes its way up to the uterus to be implanted. It's important You don't create Babies unless you're ready either.
If no condom is used Sexually Transmitted Disease may also travel from one partner to the other.