This is the term that Manhattan people use to describe the 'weekend warriors' who drive over the bridges or through the tunnel from Brooklyn and Queens (Long Island) or New Jersey to flood the best clubs. Incidentally there is a London based band called Bridge & Tunnel said to have taken their name from this American term. They have shown their affinity for the area in their record 'Borough of Kings' which is about Brooklyn and includes lyrics naming the subways that connect the area.