Mammary intercourse

Mammary intercourse (also titfuck or tittyfuck) is a sexual activity. People may do it during foreplay. It is also done as a safe sex alternative to anal or vaginal sexual intercourse (fucking). It is non-penetrative sex. It involves exciting the penis using the breasts of the partner. 
In most instances, this sexual activity involves the man placing his penis between his partner's breasts. He then thrusts while the breasts are squeezed around the penis for more excitement. Mammary intercourse is sometimes combined with oral sex (blowjob). Sometimes mammary intercourse continues to the point of ejaculation. The semen can land on the breasts, face, or in the mouth of the partner. 
Some gay males may enjoy their partners breasts. They may engage in male-male mammary intercourse if the breasts are large enough.
Several slang terms refer to mammary intercourse. These slang terms include "titfuck" or "titty fuck" in the United States. "Tit wank" or "French fuck" are slang terms used in the United Kingdom.