Evidence is simply information - facts and observations about the matter at hand.
But not all information is considered evidence, and not every piece of information may be allowed to be presented as part of a party's case. Judges and lawyers must follow the Rules of Evidence, which have been created over decades to insure a fair trial. During a trial, information may be presented that may not be considered by the jury. The judge decides what evidence is proper and admissible. The judge may allow the jury to hear certain testimony or to see particular exhibits.