Testes: The male sex glands. They are located behind the penis in a pouch of skin called the scrotum. The testes produce and store sperm, and are also the body's main source of male hormones, such as testosterone. These hormones control the development of the reproductive organs and other male characteristics, such as body and facial hair, low voice, and wide shoulders.

Also known as the testicles.

The singular of testes, the word "testis" is Latin and means "witness." In ancient times, a person providing testimony might validate it by holding the scrotum, his or another man's.