back extension

A butt that, is very flat and resembles a long back leading up to the legs.

Damn she'd be a 10 if it wasn't for that back extension.

by the watch April 13, 2015

knock the back door in and put the extension up

Polite euphemism for anal sex, just crying out to be written into an updated Carry On film based around DIY enthusiasts.

Jack Douglas : "I'll be finished as soon as I've knocked her back door in and put me extension up"
Sid James : "Hwar har har!"

by TC Raymond August 15, 2005

extension of the back

a girl with no ass

by Anonymous April 19, 2003