UK and Australia: the female genitals
US: the buttocks
As a result of these different meanings, there is bound to be confusion.
"Have you seen my Fanny?"
"I'm in love with Fanny..."
"That's my Fanny; as cute and sweet as ever!"
"What could she do? She was out on her fanny."
"We deserve a spanking, right on our fannies!"
"Just look at this little rash on her fanny."
"I'll just put it in my fanny pack."
"Danny, Danny with the big, white fanny-!"
(comes from a serviceman's vocabulary during the 1st & 2nd World Wars, i.e. "im going out to try & get myself a Fany")
and the term has developed from there to not just mean a female, but her actual sexual organs.
(this could be where the Americans get it from i.e. "im going out to try & get myself some ass (FANY)"
During the First World War, FANYs ran field hospitals, drove ambulances and set up soup kitchens and troop canteens, often under highly dangerous conditions.
so therefore were mostly the only female's the sex starved soldiers came into contact with.
see > www.fany.org.uk
American English: fanny = ass
That drunk limey let Jane stick anal love beads in his fanny.
That drunk limey blew his load across America when I shoved my finger in his fanny.