It's the medical term for when the foreskin of the penis doesn't retract fully. The term is a bit confusing, because it's used to describe this situation when it is both physiologically normal (babies and young children) and a pathologic problem that can cause infertility and recurring infections ( in adults) .

Attitudes towards phimosis have changed over the last century or so. At one time, routine neonatal circumcision was thought best to prevent adult phimisis. Research on the matter showed that routine neonatal circumcision (an invasive and painful procedure) was rarely necessary though; phimosis in children usually resolves itself, typically by age 3 and nearly always by age 7.

When boys reach the age of 7 or so and cannot retrct the foreskin yet, different courses of action may be advised depending on individual circumstances. Young boys may be encouraged to "fiddle" with themselves to encourage the foreskin to pull back fully. If the child is experiencing infections, antibiotics may be prescribed. If there is pain, recurring infections or difficulty in urinating, then medical circumcision may be resorted to.