The Central Criminal Court of England and Wales, commonly referred to as the Old Bailey after the street on which it stands, is a criminal court building in central London. The street outside follows the route of the ancient wall around the City of London, which was part of the fortification's bailey, hence the metonymic name.
Metonymic: figure of speech in which the name of an object or concept is replaced with a word closely related to or suggested by the original, as “crown” to mean “king”