The standard of proof refers to the level or degree of evidence required in a legal proceeding to establish the guilt, liability, or truth of an assertion. It is used to determine whether the prosecution has met its burden of proving the defendant's guilt beyond a reasonable doubt, or whether the plaintiff has proven their case by a preponderance of evidence. The standard of proof varies depending on the severity of the charge or claim being made and can range from "beyond a reasonable doubt" to "by clear and convincing evidence," or even just "a preponderance of evidence."