Chances are you first started calling dibs back when you were a kid on the playground. Coincidentally, the playground is exactly where the phrase is believed to have menu
A quorum is the minimum number of people who must be present to pass a law, make a judgment, or conduct business. Quorum requirements typically are found in a court, legislative assembly, or corporation (where those attending might be directors or stockholders).
In the House of Representatives, the quorum was amended down to one-fifth by the House of Representatives (Quorum) Act 1989, which means the quorum of the current House of 150 MPs is 30 MPs. In the senate, the quorum was amended down to one-quarter by the Senate (Quorum) Act 1991, so 19 senators is a quorum.