Phimosis is a medical disorder of the penis "...in which the foreskin cannot be retracted to reveal the glans penis. It is due to tightness or narrowing of the foreskin opening." Elective circumcision, under appropriate anesthesia, is the preferred treatment.
A variant is paraphimosis, in which "the foreskin, once retracted, cannot return to its original position. If this condition persists, it can lead to painful constriction of the glans penis, swelling, and impaired blood flow to the penis."