Ejaculation is the process by which semen is expelled from the penis.
Sperm cells mix with fluid from the prostate and seminal vesicles. This fluid gathers in part of the urethra. It’s a distinct sensation, which a guy can feel a few seconds before he comes. It’s called the point of no return, because he will climax, no matter what he does.
The good feeling a guy gets at the moment of expulsion is called orgasm.
The expulsion of this fluid takes a few seconds. It’s expelled in 3 to 10 spurts.
The first ejaculation normally takes place between the ages 11 and 16. Once the sperm factory is in operation orgasm goes hand in hand with ejaculation. Before this time a guy can have orgasms, but without ejaculating.
When guys ejaculate during their sleep it’s called a ‘wet dream.’

My semen is not expelled forcefully, but it’s just leaks out. What can I do?
When I masturbate several times in a row there is no semen. How come?

See also: semen