What is a filibuster?
It's when a senator, or group of senators, attempts to block or delay action on a bill or nominee under consideration in the Senate. In order to stop the filibuster, Senate leaders can invoke a procedure called cloture.
So what happened on Thursday?
The Senate changed its rules regarding filibusters on votes to confirm most judicial and executive branch appointments.
Under the old rules, at least 60 votes were required to invoke cloture, and if cloture passed, the filibuster would end.
But on Thursday, Senate Democrats took a series of steps to change how the filibuster applies to confirmation votes. Under the new rules, the vote to end a filibuster/invoke cloture only requires a simple majority vote of the 100 senators. Senators may still opt to delay a bill or nomination by filibustering the action, but only 51 votes will be needed to invoke cloture. (And yes -- 51 is required even if some senators are absent or seats are vacant.)
This change doesn't apply to nominees to the U.S. Supreme Court. And the change doesn't apply to pieces of legislation -- under the current rules, at least 60 votes will be required to end the filibuster of a bill.
So what does this mean?
It means that federal judge nominees and executive branch appointments can be confirmed by a simple majority of senators, rather than the 60-vote supermajority that has been required for more than two centuries.
And why does this matter?
For starters, it's one of the most fundamental changes in Senate procedure ever.
In the short-term, it makes it much more difficult for Democrats and Republicans to work together on a host of issues -- the budget, the farm bill, a defense policy bill. Republicans once willing to negotiate on those measures now might resist because of the unilateral steps taken by Democrats.
Sen. John McCain (R-Ariz.), who sought to stop the changes, said Democrats “are going to have trouble in a lot of areas, because there’s going to be a lot of anger.”
But Democrats say that Republicans were needlessly blocking qualified people from filling judicial vacancies and key government positions. In the words of Sen. Christopher Murphy (D-Conn.), one of the senators pushing most aggressively for the change: "I think democracy is broken when the minority can hold up legislation or nominees with only 40 votes."
But Republicans are furious and say Democrats will learn to regret the changes when they eventually become the minority party.
"Democrats won’t be in power in perpetuity," Sen. Richard Shelby (R-Ala.) said Thursday. "This is a mistake, a big one for the long run.... I think it changes the Senate tremendously in a bad way."
This also matters because it opens the door to more changes in Senate procedure. Murphy and other liberal senators now want the new 51-vote threshold to apply to cloture on all legislation. That would make the Senate another version of the House, where simple majority votes have always been the standard.
I’m totally confused by the filibuster. Should I feel bad?
Perk up -- you’ve got plenty of company. A 2010 Pew Research poll found that only 26 percent of Americans knew the number of votes needed to break a filibuster.
Paul Kane and Capital Insights polling analyst Scott Clement contributed to this report.