The urethra is a tube that connects the urinary bladder to the outside of the body. The function of the urethra is excretory, to pass urine to the outside (in both sexes) and, also, reproductive, as a passage for sperm in the male.
In females, the urethra opens between the clitoris and the vaginal opening and is about 1-1.5 inches long. In males, the urethra opens at the end of the penis and is about 8 inches long. The external urethral sphincter is the skeletal muscle that allows you voluntary control over micturition.
Hypospadias is a form of abnormal development of the urethra in the male, where the opening is not quite where it should be (it occurs lower than normal in hypospadias). If the urethra develops between the penis and the scrotum, it's a chordee.
Infection of the urethra is urethritis, said to be more common in females than males. Urethritis is a common cause of dysuria.