Phimosis: A condition whereby the foreskin of the penis is too tight.
The penis itself consists of a cylindrical shaft with a rounded tip which is called the glans. The foreskin, or prepuce, is the fold of skin that covers the glans.
Phimosis is medically defined as "stenosis (tightness) of the preputial ring with resultant inability to retract a fully differentiated foreskin." In other words, the foreskin is so tight it cannot be pulled back completely to reveal the glans.
Phimosis is a common condition, usually causes no problems, and nothing needs be done. If phimosis causes obstruction of the urinary stream, hematuria (blood in the urine), or pain, this can be a urologic emergency and require surgery to relieve the phimosis.
The word "phimosis" came from the Greek "phimos" which was the muzzle on an animal and the noseband on the bridle of a horse.