Bukkake is a niche sexual act where a large group of men ejaculate on a woman. More recently, pornographic movies have expanded to have a male on the receiving end, or lesbians that squirt when they orgasm cover another individual in their fluids.
In the 1980's, all actual images of genitalia in Japanese porn were required to be pixelated. Kazuhiko Matsumoto, a director, noticed that since the genitalia was pixelated, filmmakers tended to concentrate on breasts and the actresses faces. Since spurts of semen were not banned or did not require pixelation, he had a woman receive load after load from the males. His film caught on, and more bukkake pornos were produced. Their popularity spread to the United States.
The United States popularity did not create a large market, as the producers had hoped. Some customers felt the woman was reduced to an object or in a position of subordination. Others liked bukkake for just this reason. Some people consider it a form of symbolic group rape. Many women consider it a degrading practice, while others incorporate in their BDSM sessions.
Bukkake means "heavy splash" in Japanese. There is a dish called bukkake udon where the broth is quickly poured on the udon noodles, splashing on the table in the process.