A double bounce serve or return is when you can get the ball to bounce twice (or more) on the opponent's side of the table.
For a double bounce serve, you would want to keep the ball low and short, and may use a variety of spins while still making the ball double bounce. These are effective because it is hard to attack a ball that doesn't pass the end of the table. Of course if you leave the ball high, the receiver may still be able to attack.
You can also return the opponent's serves and rallies using the double bounce concept, keeping it short and low so it is difficult or impossible to attack.
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