A quorum call or call to quorum is a parliamentary procedure used to delay a vote or otherwise slow down the deliberations of a parliamentary body. Since attendance at debates is not mandatory in most legislatures, it is often the case that a quorum of members is not present while debate is ongoing. In many bodies, motions such as amendments, tabling, and recommitment may be approved in the absence of a quorum, provided no member then present objects. ...
http://en.wikipedia.org/wiki/Quorum_call