A hybrid electric bus is a bus that combines a conventional internal combustion engine propulsion system with an electric propulsion system. These type of buses normally use a Diesel–electric powertrain and are also known as hybrid Diesel–electric buses.

A double-decker bus or double-deck bus is a bus that has two storeys or decks. Double-deckers are primarily for commuter transport, but open-top models are used as sight-seeing buses for tourists, and there are coaches too for long-distance travel. They appear in many places around the world but are presently most commonly used as mass transport in cities of Britain and Ireland, in Hong Kong, and in Singapore.