What is the term for when a senator holds the floor in the Senate, continuing to speak in order to delay or prevent a vote?

The term "filibuster" refers specifically to a tactic used in the Senate where a senator takes the floor and speaks for an extended period to impede the legislative process, thereby delaying or preventing a vote on a particular bill or issue. This often requires a supermajority to invoke cloture and end the debate, thus allowing a vote to take place. The filibuster is a significant tool within the Senate's procedural rules, illustrating how individual senators can wield considerable power over legislative outcomes by prolonging debate.

The other terms listed do not apply in this context. Riders refer to amendments added to legislation that may be unrelated and are inserted to pass additional measures. A pocket veto is a mechanism by which the president can effectively veto a bill by taking no action on it when Congress adjourns, while withdrawal does not pertain to Senate procedure regarding voting delays. Understanding the filibuster is crucial in analyzing how and why certain legislation might struggle to pass through the Senate.