What is semen? Semen is a whitish fluid that is expelled from the urethra (tube inside the penis that also carries urine) in the ejaculate. The ejaculate is the product of the mixture of secretions from the testicle, where the sperm are produced, with the secretions of the prostate, seminal vesicles and bulbourethral glands. Normally every cubic centimeter of semen contains millions of sperm (sperm), but most of the volume is due to the secretions of the glands of the male reproductive organs (prostate and seminal vesicles, fundamentally).