Definition: Semen or cum is an organic fluid (also known as seminal fluid) that is usually expelled by having a cumshot inside a vagina, anus or mouth of those women (or men) who enjoy swallowing cum.
It is produced by testicles and it is in charge of fertilizing women's ovaries.
The process of ejaculating the semen is called ejaculation or cumshot. The regular volume produced by cumshot is from 2 to 5 ml. All those cumshots producing much less than 1,5 ml (hipospermia) or more that 5.5 ml (hiperspermia, like the huge cumshots of Peter North) are probably not normal.
A lower volume of cum can be produced after cumming many times, while the higher one can be produced after a long abstinence.
In the next link you can watch some facial cumshots of women who enjoy swallowing cum.