One legal term that has always stumped me is the meaning of "beyond reasonable doubt". It's not a phrase that we use in everyday speech, so its meaning doesn't come readily to mind. Apparently, it means something less than "absolutely certain" and something more than "reasonably certain". What's worse is that judges cannot attempt to define it for the jury. Doing so can lead to a mistrial. https://www.ruleoflaw.org.au/beyond-reasonable-doubt/