A scooter is a small wheeled vehicle. A child's scooter has two wheels and is powered by pushing one foot against the ground.
The word scooter covers a wide variety of vehicles. There's the kick scooter that you can use for rolling down the sidewalk, and the motor scooter that's essentially a lightweight, gas-powered motorcycle. Mobility scooters are used by people who need a little extra help getting around, either in the form of a wheeled walker that can be kneeled on, or a motorized wheelchair. The word scooter was originally shorthand for motor scooter.