What's a filibuster?
The filibuster - used this week by Republican Sen. Rand Paul to oppose John Brennan's nomination as CIA director - is a parliamentary tactic used to block or delay legislative action.
Using a filibuster, a senator can essentially hold the floor to prevent a bill from coming to a vote.
Filibusters - from the Dutch word for "pirate" - were popularized in the 1850s and continue today in the Senate on the thinking that any senator should be able to speak as long as necessary on an issue, according to Senate historians. Paul's filibuster lasted nearly 13 hours, ending early Thursday.
Rules were passed long ago to limit debate in the larger House of Representatives.
In 1975, the Senate reduced the number of votes required to end the debate - an action called "cloture." Cloture requires a three-fifths vote, or 60 of the current 100 senators.
Filibuster tactics have varied over time. During the 1930s, Senator Huey P. Long of Louisiana used the filibuster against bills that he thought favored the rich over the poor - taking up the time by reciting Shakespeare and reading recipes for "pot-likkers." He once held the floor for 15 hours, but the record for the longest individual speech goes to South Carolina's Strom Thurmond. Thurmond filibustered for 24 hours and 18 minutes against the Civil Rights Act of 1957, Senate historians say.