Presidents and chairpersons of organizations often use a gavel while running a meeting. But a leader doesn't just rap indiscriminately whenever she wants quiet or to signal the meeting's end or a vote's passing. According to parliamentary procedure, the rules for running a meeting, it matters how many taps of the gavel you use; each number has a meaning.
There are three possibilities when a president taps the gavel one time. It tells the members to be seated. It is used after the president announces the results of the vote on a motion or item of business. The members then know it is time to move on to another topic. The president also taps the gavel once after announcing the meeting is adjourned. In all cases, it's a quick way to get the attention of the meeting's participants
The president taps the gavel twice to call the meeting to order.
When the president taps the gavel three times, it instructs the members to stand up. It may be used before the Pledge of Allegiance is recited, for example.
When the president uses a series of sharp taps, he is trying to maintain or regain order at a meeting.
You can find more information about the use of the gavel in the book "Robert's Rules of Order."