Usually the final bit of a porn movie where the guy with a huge cock pulls out of the actress's pussy and shoots his jizz all over her face. Often said actress will hold her mouth wide open and stare up at the guy imploringly, and frequently then make a big show of rolling it around in her mouth, blowing bubbles, etc.
A slang term used describe male ejaculation of semen from the penis, or female ejaculation of fluid from the vagina. Mostly refers to male ejaculation.
She sucked his dick so good he gave her a massive cum shot down her throat.