Here are brief explaination of Jac, thanks to Gaku at http://www.gaktradinginc.com/01home/02glossary.htm


Jac: The symbol of "Replay" turns into a Jac during the Bonus Game.

Jac Game: A Jac Game pays out 15 tokens. After a Jac-in, the machine automatically keep bringing on Jac Games.

Jac-in: To enter an Eight-Jac-Games by hitting three Jacs during the Bonus Game.


He goes into a more detailed explaination when you visit the Glossery.