Phimosis is a condition where the foreskin of the male penis cannot retract fully, preventing it from being pulled back over the glans. There are two main types - infantile/congenital phimosis where infants are born with a tight foreskin, and acquired phimosis in adults caused by infections under the foreskin like balanitis. Diagnosis involves physical examination of the penis and foreskin. Treatment options include circumcision, steroid creams, or stretching the foreskin gradually with devices. Complications can include pain urinating and recurring infections if not treated.