beyond a reasonable doubt

Outside legal framework it's similar to saying 'I'm either certain or as close to certain as possible' -inside legal framework, it's a frame of mind, the universal standard of proof used to decide if a defendant is guilty or not. To find a defendant guilty a juror or judge must reach a frame of mind that leaves them with no doubt or at least almost no doubt that a defendant is guilty as charged. Therefore, beyond a reasonable doubt. Information that leads factfinders to this mind frame must be directly related to particular case, not from outlying information unrelated to case in question, usually arising from attempts to tar/slime the defendant.