An Opinion, in regards to it's judicial definition, is basically what the judge writes down as the definitive explanation of the decision the court has made.

In situations where more then one judge rules on a single court (ie judges in the court of appeals) the opinion in appellate decisions can take several forms- One judge will write the opinion for all of the other presiding judges if all the judges agree on the result. In instances where the judges are split, the formal decision will be based upon the view of the majority (one of which will write the majority opinion). The judges who did not agree with the majority may write separately opinions to present their views, where-as their opinion will disagrees with the majority opinion because of the reasoning and/or the principles of law (that the majority used to decide the case). Then, there is sometimes a concurring opinion, which agrees with the decision of the majority opinion, but offers further comment or clarification or even an entirely different reason for reaching the same result. Only the majority opinion can serve as binding precedent in future cases. See also precedent.