Definition from Nolo’s Plain-English Law Dictionary
A term that is often mistakenly equated to a plea of "not guilty." Innocence is not a legal term, but rather a philosophical, moral, or religious expression of nonresponsibility. By contrast, a not guilty plea simply means that the defendant is demanding that the prosecutor prove every part of the charged crime beyond a reasonable doubt. Many defendants who plead (and are found by the jury to be) not guilty are probably not innocent under any reasonable understanding of that term. Instead, the prosecutor may have simply failed to produce enough compelling evidence, failing to convince the jury beyond a reasonable doubt.