A threshold or burden of proof in criminal cases, and a requirement in most modern criminal law systems, which requires the prosecutor or district attorney to prove to the trier of fact to be sure, not certain, of the accused guilt, before convicting.
For years, the Courts were reluctant to define this term, hoping that it was self-evident.
However, in 1997, the Supreme Court of Canada, in R v Lifchus 3 SCR 320 (published at canlii.org/en/ca/scc/doc/1997/1997canlii319/1997canlii319.html), suggested these explanatory words:
"The accused enters these proceedings presumed to be innocent. That presumption of innocence remains throughout the case until such time as the Crown has on the evidence put before you satisfied you beyond a reasonable doubt that the accused is guilty.
"What does the expression “beyond a reasonable doubt” mean? The term “beyond a reasonable doubt” has been used for a very long time and is a part of our history and traditions of justice. It is so engrained in our criminal law that some think it needs no explanation, yet something must be said regarding its meaning.
"A reasonable doubt is not an imaginary or frivolous doubt. It must not be based upon sympathy or prejudice. Rather, it is based on reason and common sense. It is logically derived from the evidence or absence of evidence.
"Even if you believe the accused is probably guilty or likely guilty, that is not sufficient. In those circumstances you must give the benefit of the doubt to the accused and acquit because the Crown has failed to satisfy you of the guilt of the accused beyond a reasonable doubt. On the other hand you must remember that it is virtually impossible to prove anything to an absolute certainty and the Crown is not required to do so. Such a standard of proof is impossibly high.
"In short if, based upon the evidence before the court, you are sure that the accused committed the offence you should convict since this demonstrates that you are satisfied of his guilt beyond a reasonable doubt."