A booster may mean:

• a person who promotes his or her town or region – see boosterism
• a booster rocket used in space flight to achieve escape velocity
• a co-channel repeater in broadcasting, used to improve signal strength
• a booster seat, used by children after outgrowing a highchair
• a booster shot – a follow-up to a vaccine
• a booster engine - extra cylinders on a steam locomotive, driving the trailing truck or a tender truck, to give more power on starting
• a booster unit - a cabless diesel locomotive used to boost the power of a locomotive consist but incapable of being used on its own. See B unit.