English Idiom: Fly the coop
To fly the coop means to escape. Think about chickens on a small farm. The little building in which people keep chickens is called a chicken coop. Sometimes when the door is open, a chicken will escape.
If you are in a situation that you do not like, such as a boring meeting or dinner party you could use a phone call from your babysitter as an excuse to fly the coop or escape that unpleasant situation.
Prisoners in jail are in a situation similar to the chickens in a coop.
I would think, most prisoners dream about flying the coop.
Some are successful, but they usually get caught by the long arm of the law, eventually.