Rule 12(b)(6) is a provision under the Federal Rules of Civil Procedure that allows a defendant to seek dismissal of a complaint for failure to state a claim upon which relief can be granted. This rule emphasizes the necessity of sufficient factual allegations in a complaint, establishing that mere legal conclusions or vague assertions are not adequate to survive a motion to dismiss. It serves as an essential mechanism for ensuring that only legally sufficient claims proceed in court, promoting judicial efficiency and protecting defendants from frivolous lawsuits.