A filibuster (from Early Modern English, c. 1580: filibutor, "pirate") is a parliamentary procedure where debate over a proposed piece of legislation is extended, allowing one or more members to delay or entirely prevent a vote on the proposal. It is sometimes referred to as "talking out a bill" or "talking a bill to death" and characterized as a form of obstruction in a legislature or other decision-making body.
The English term "filibuster" is derived from the Spanish filibustero, itself deriving originally from the Dutch vrijbuiter, "privateer, pirate, robber" (also the root of English ""). The Spanish form entered the English language in the 1850s, as applied to military adventurers from the United States then operating in Central America and the Spanish West Indies such as William Walker.
William Safire, following the etymology in the Oxford English Dictionary, states that the term in its legislative sense was first used by Rep. Albert G. Brown, (D-MS) in 1853, referring to Abraham Watkins Venable's speech against "filibustering" intervention in Cuba. However, this usage was merely the first use of the word in the congressional record, in this case in reference to a filibuster action in Cuba, that is, a private military adventure not sanctioned by the government. As found in the "Online Etymmological Dictionary", the word most likely extends from the idea that a single Senator can pirate debate. The word originally referred to "the senator who led it; the maneuver itself so called by 1893. Not technically restricted to U.S. Senate, but that's where the strategy works best."
One of the first known practitioners of the filibuster was the Roman senator Cato the Younger. In debates over legislation he especially opposed, Cato would often obstruct the measure by speaking continuously until nightfall. As the Roman Senate had a rule requiring all business to conclude by dusk, Cato's purposefully long-winded speeches were an effective device to forestall a vote.