"Without prejudice..." means "the said statement is not an implicit waiver about..."
This reservation is used when a provision may be interpreted in a way that limits any other right that is not expressly mentioned in the sentence.
Some scholars agree that this legal term is actually meaningless, because an interpretation is limited by the facts and morality any way. Any such reservation would not completely avoid interpretation of a contractual provision, nor its absence would grant either party a universal power to interpret the contract.