Coaster brakes aka back-pedal brakes, actuated by pedalling the cranks backward.
Coaster brakes are an arrangement of wedges that are physically inside the hub of a bike's rear wheel.
These brakes are common on young children's bicycles because smaller kids lack the hand strength to actuate a hand-lever for a brake. Additionally a kids bike is more appealing if it can do long "mad-skidz" which are hard or impossible with a hand brake.
You'll never find a coaster brake in a front wheel because they require the drive train for activating.
Other visually similar but different brakes could include [band-brake] or [drum-brake] but these are not pedal-actuated.
If the pedals and wheel are locked and can't freewheel, then that is a [fixed-gear] and not a coaster brake.