The hearsay rule is a legal principle that prohibits the use of out-of-court statements as evidence to prove the truth of the matter asserted. This rule is designed to ensure that evidence presented in court is reliable and trustworthy, as hearsay statements are generally considered less credible due to the lack of opportunity for cross-examination. Understanding the hearsay rule is essential in civil litigation, as it can significantly affect the admissibility of evidence and the overall outcome of a case.