Hybrid Electric Vehicles use an internal combustion engine in conjunction with an electric motor, combining gas and electricity for high fuel efficiency and low emissions. These vehicles operate similarly to conventional cars and recharge their electric source through regenerative braking, saving energy typically lost during braking or accelerating on highways and straight roads.
https://afdc.energy.gov/vehicles/electric_basics_hev.html
https://www.nrel.gov/research/transportation-hybrid-electric.html