This type of sex is frequently practiced with a false sense of security. Keep in mind that oral herpes can be transmitted to the genitalia and in some people HPV can be transmitted this way. Outer sex limits the risk of pregnancy and sexually transmitted disease if there are no open sores on the external genitalia and if ejaculation occurs away from the opening of the vagina. Outer sex can be difficult to control and the desire for more may lead to intercourse. Keep this in mind before engaging in outer sex without a handy supply of condoms.
Vaginal sex is penetration of the vagina by the penis.
This is traditionally what is thought of as intercourse. In the female virgin the entrance to the vagina is often partially blocked by a membranous tissue called the hymen. The size of the hymen varies greatly among females. Some virginal girls have virtually no hymen and others have enough tissue to make using tampons difficult. The presence of the hymen will sometimes make the first vaginal intercourse painful and bleeding is not unusual.