A motion to dismiss is a formal request made by a party in a lawsuit asking the court to dismiss the case on specific grounds, typically asserting that the complaint fails to state a claim upon which relief can be granted. This motion can challenge the legal sufficiency of the claims presented in the complaint and is usually filed before the responding party answers. It plays a crucial role in filtering out cases that lack merit early in the litigation process, thus streamlining court proceedings and conserving judicial resources.