Tip No. 15 To paraphrase Shakespeare’s Hamlet “With prejudice” or “without prejudice” … that is the question

The term “without prejudice” sometimes means that there is no decision of the controversy on its merits. Thus, where a motion is denied “without prejudice” it is meant as a declaration that no rights or privileges of the party concerned are to be considered as waived or lost, except insofar as they may be expressly conceded or decided, and will prevent the decree of dismissal from operating as a bar to a subsequent suit on the same cause of action. Alternatively, the term "without prejudice" may mean that the decision was on the merits, on the grounds the moving party failed to satisfy the statutory requirements; however, the moving party is not precluded from pursuing another method to litigate the claims. 

A dismissal “with prejudice” is an adjudication on the merits and final disposition, barring the right to bring or maintain an action on the same claim or cause; it is res judicata as to every matter litigated. 

That being said, in practice a judgment of dismissal without qualifying words is presumed to be on the merits (i.e., with prejudice).