Semen, also known as seminal fluid, is a bodily fluid that contains spermatozoa. Spermatozoa are secreted by the male gonads and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. In placental mammals, semen also contains secretions from the male accessory glands and is discharged from the penis through the urethral orifice during ejaculation. In humans, seminal fluid contains several components besides spermatozoa: proteolytic and other enzymes as well as fructose are elements of seminal fluid which promote the survival of spermatozoa and provide a medium through which they can move or "swim". The fluid is adapted to be discharged deep into the vagina, so the spermatozoa can pass into the uterus and form a zygote with an egg.

Semen collection refers to the process of obtaining semen from human males or other animals with the use of various methods, for the purposes of artificial insemination, or medical study. Semen can be collected via masturbation, prostate massage, artificial vagina, penile vibratory stimulation (vibroejaculation) and electroejaculation. Semen can be collected from endangered species for cryopreservation of genetic resources.