A non-majoritarian feature in the U.S. Senate is extended debate (filibuster). Senators can talk about anything for as long as they like when a bill is on the floor. This gives individual Senators a great deal of leverage. To end or prevent filibusters, Senate can vote to invoke cloture (end debate). Sixty votes are required to invoke cloture. If cloture is invoked, debate is limited to 30 additional hours. A practical implication of this is that most legislation requires 60 votes.
Senate rules and customs limit filibusters in two ways: reciprocity; and a Senator can issue holds. Reciprocity means that one Senator will not hold a filibuster out of reluctance to endure an opposition filibuster. Holds stop the bill from coming to the floor for a vote, so that agreements can be negotiated beforehand.