Ejaculation is the act of expelling semen (called the ejaculate) from the body. It occurs after the penis has been stimulated by sexual activity or masterbation and is the result of the male orgasm. Ejaculation itself typically occurs after five to seven minutes of stimulation and lasts for several seconds.
Semen contains sperm which is of course a vital component in reproduction. However sperm is not always present in semen and this may be due to the fact the man has had a vasectomy or down to a medical condition, such as azoospermia.