Semen () is the fluid that comes out from the end of a man's penis when he has an orgasm (the height of sexual excitement) and ejaculates. It is usually a white or yellowish, sticky substance made up of sperm (male cells for sexual reproduction) floating in a fluid called seminal plasma that has water and different chemicals in it. Normally, an ejaculation makes between 1.5 and 5 millilitres (up to one teaspoonful) of semen.