A slightly alkaline fluid (pH 7.2–7.6) containing sperm and various secretions that is produced by a male mammal during copulation and is introduced into the body of the female by ejaculation. Spermatozoa are produced by the testes and the secretions by the prostate gland, seminal vesicles, and Cowper’s glands. Semen also contains enzymes that activate the sperm after ejaculation.