When I first heard the term 'filibuster', I was reading a novel for school. I tried to derive its meaning from the context of the novel and what I got was that it was someone who tries to oppose government. And in a way, that was partly correct. But it doesn't completely encapsulate what a filibuster does. So here's what it is:
Generally speaking, a filibuster impedes legislative work by exploiting the rule of unlimited debate. Basically, a legislative body (think Parliament or the US Senate) can discuss something for as long as they’d like until a decision is made. As long as the discussion is being held, a decision is never made, and political obstruction has occurred.
There are other questions regarding these filibusters. From one point of view, one can say that what filibusters do is illegal while others only say it's unethical. Still others view it as a legitimate political tactic. For more information on it, check out Sporcle.
(Image credit: "Mr. Smith Goes to Washington", Columbia Pictures via Sporcle)