As Gene would say... You HAD to ask!!

Hold (on an individual table) is the difference in the money dropped vs. the change in chips in the rack. As an easy example, you buyin at BJ for $100, play a while up & down, and eventually leave the table with $80, heading to the cashier. Your net $20 loss is a 20% hold. Holds are also calculated for each shift, for table games vs. slots, for the whole casino, etc.

Hold is much different than Handle (or Action). Handle is the total value of all your bets. In the above example, you may have placed 50 $5 bets, for a total of $250 handle or total action, even though you walked away just $20 down.