The obligation of a party to introduce evidence that persuades the factfinder, to a requisite degree of belief, that a particular proposition of fact is true. In civil cases, a party's burden is usually "by a preponderance of the evidence." In criminal cases, the prosecution's burden is "beyond a reasonable doubt."
The burden of persuasion is comprised of two elements: the facts a party must plead and prove in order to prevail on a particular issue; and how persuasively the party must prove those facts.