What is Beyond A Reasonable Doubt?

Legal Definition
Evidence that is beyond reasonable doubt is the standard of evidence required to validate a criminal conviction in most adversarial legal systems. This means that the proposition being presented by the prosecution must be proven to the extent that there could be no "reasonable doubt" in the mind of a "reasonable person" that the defendant is guilty. There can still be a doubt, but only to the extent that it would not affect a reasonable person's belief regarding whether or not the defendant is guilty. Beyond "the shadow of a doubt" is sometimes used interchangeably with beyond reasonable doubt, but this extends beyond the latter, to the extent that it may be considered an impossible standard. The term "reasonable doubt" is therefore used.
-- Wikipedia