A demurrer is a legal pleading that challenges the sufficiency of an opponent’s legal claim or defense, asserting that, even if the facts alleged are true, they do not constitute a valid legal claim or defense. Essentially, it argues that the case should be dismissed because the pleading fails to state a cause of action or defense that is legally recognized. In modern U.S. legal practice, demurrers have largely been replaced by motions to dismiss (e.g., under Rule 12(b)(6) in federal courts), but the term is still used in some jurisdictions, particularly in California state courts. It does not dispute the facts but focuses on the legal validity of the claim.