"The filibuster is widely viewed as one of the Senate's most distinctive procedural features. Today, the term is most often used to refer to Senators holding the floor in extended debate. More generally, however, 'filibustering' includes any tactics aimed at blocking a measure by preventing it from coming to a vote. As a consequence, the Senate has no specific 'rules for filibustering.' Instead, possibilities for filibustering exist because Senate rules deliberately 'lack' provisions that would place specific limits on Senators' rights and opportunities in the legislative process. In particular, those rules establish no generally applicable limits on the length of debate, nor any motions by which a majority could vote to bring a debate to an end, or even limit it. The only Senate rule that permits the body, by vote, to bring consideration of a matter to an end is paragraph 2 of Rule XXII, known as the 'cloture rule.' Invoking cloture requires a super-majority vote (usually 60 out of 100 Senators), and doing so does not terminate consideration, but in most cases only imposes a time limit. Cloture also imposes restrictions on certain other potentially dilatory procedures. In recent years, as a result, cloture has increasingly been used to overcome filibusters being conducted not only by debate, but through various other delaying tactics. This report discusses major aspects of Senate procedure related to filibusters and cloture. The two, however, are not always as closely linked in practice as they are in popular conception. Even when opponents of a measure resort to extended debate or other tactics of delay, supporters may not decide to seek cloture (although this situation seems to have been more common in earlier decades than today). In recent times, conversely, Senate leadership has increasingly made use of cloture as a normal tool for managing the flow of business on the floor, even at times when no evident filibuster has yet occurred."
CRS Report for Congress, RL30360