The autoplunger is a pinball
mechanism used on some tables to allow the machine to automatically deliver a ball into play.
Autoplungers consist of a solenoid and some sort of kicker, mounted in the plunger lane. They may be used as a replacement or supplement to the typical manual spring-loaded plunger.
They are often used on a game where certain modes require additional balls to be served up for multiball from a virtual lock, wherein balls are not physically held on the playfield, but are only counted in software. Examples of this are the locks on South Park, Medieval Madness, and Attack From Mars.
Games which use an autoplunger must often implement Skill Shot at the beginning of a ball differently. On games with a manual plunger, the skill shot typically relies on launching the ball with a very carefully controlled amount of force. On games with an autoplunger, the Skill Shot may either be dependent on timing, as found on Terminator 2: Judgement Day, Star Trek: The Next Generation, or Dracula; or it may serve the ball up to the flippers for a time limited attempt to make a shot on the playfield.
The hybrid auto/manual plunger appears on a handfull of games, such as South Park. It consists of a forked yoke mounted around the manual plunger's rubber tip, which ordinarily does not contact the ball; however, when needed, it gets kicked forwards and launches the ball.
Games with an autoplunger will typically relaunch a ball which accidentally somehow gets back into the plunger lane, and will automatically retry every second or so to launch a ball which hasn't exited the lane. This tends to happen a lot if the solenoid has gotten dirty.
A feature commonly associated with the autoplunger is the ball saver. In the event of a quick drain at the start of a ball, the machine will courteously serve up another and automatically kick it into play for you. This is also implemented on some machines with manual plungers. You usually cannot use it to collect the skill shot twice.