The kickback feature in a pinball machine allows the player to continue where they would have otherwise drained out of either outlane. A solenoid fires (not unlike an auto-plunger) against the ball, which quickly shoots it up the outlane and back into the playfield. For many games, this is enabled as part of the ball save and given to the player as a reward during normal play.
The solenoid is mounted in the apron area, and a lane guide will need to be mounted for the ball to properly shoot upward and out. Normally there is a playfield lamp in the outlane to indicate to the player kickback is active.