What exactly does beyond a reasonable doubt mean?

Beyond a reasonable doubt is hard to quantify, but it basically means that the prosecution has removed nearly all doubts as to whether the defendant committed the crime. Many states define reasonable doubt in their codes or in their common law (in their judicial opinions). For example, an Ohio law defines “reasonable doubt” as follows:

“Reasonable doubt” is present when the jurors, after they have carefully considered and compared all the evidence, cannot say they are firmly convinced of the truth of the charge. It is a doubt based on reason and common sense. Reasonable doubt is not mere possible doubt, because everything relating to human affairs or depending on moral evidence is open to some possible or imaginary doubt. “Proof beyond a reasonable doubt” is proof of such character that an ordinary person would be willing to rely and act upon it in the most important of the person’s own affairs.