double-decker bus

A New Routemaster double-decker bus in London

A double-decker bus is a bus that has two storeys or decks. Double-deckers are used primarily for commuter public transport, but there are coach variants for long-distance travel and open top buses that are most commonly used as sightseeing buses for tourists. They appear in many places around the world, but are presently most commonly used as mass transport in major cities.