Any vehicle is a hybrid when it combines two or more sources of power. Hybrid cars usually run off a rechargeable battery and petrol.
Hybrid engines are built smaller to accommodate the 99% of time when not going up hill or accelerating quickly. They use the battery to provide extra acceleration power when needed.
When the car is stopped, hybrid petrol motors can shut off, and run off their electric motor and battery.
Hybrid cars often recover braking energy and use it to charge the battery, termed "regenerative braking"
In the UK the Toyota Prius is the best selling hybrid. Honda's Civic is a recent entry, as are the Lexus GS450 and RX400.
