It is the bit of skin between your scrotum and your anus. It can also be used to insult people.

Anatidaephobia is defined as a pervasive, irrational fear that one is being watched by a duck. The anatidaephobic individual fears that no matter where they are or what they are doing, a duck watches.

Anatidaephobia is derived from the Greek word "anatidae", meaning ducks, geese or swans and "phobos" meaning fear.

male anatomy - the area of the sin between the scrotum and the rectum

the space between ones legs, betwen the anus hole and the bollock sack on a man
the main area where arse hair grows.

The hair that grows off the gooch not the gooch itself!