Cloture is a rule in the Senate that limits the time for debate for a bill. It is usually used to end a filibuster (a process by which Senators can debate a bill endlessly, in an attempt to keep it from passing. Filibusters had their heyday in the late 1880s and early 1900s. Democratic Louisiana Senator Huey P. Long once held the floor by continuing to talk for 24 hours straight (he was opposed to the Civil Rights Act)). It can also be used to prevent a potential filibuster.
The Senate can prevent this by invoking cloture. That happens when 60 Senators vote for it.
The rule was started in 1915, under President Wilson. Since that time, it has been invoked only 5 times.
The current vote, on Saturday, November 21, marks the sixth time.