A postnuptial agreement (also known as a 'postnup') is an agreement between two people after they have gotten married or entered into a civil partnership. It sets out the property and money that belong to each person before the marriage or civil partnership and clarifies what is intended to remain the property of that person after the marriage/civil partnership itself.
If you and your spouse or civil partner have assets which each of you would like to own as individuals rather than jointly, record these assets in a postnup. This will ensure that any assets (be it property, cash or heirlooms) owned before marriage or civil partnership will be owned by the individual and not jointly. This postmarital or post-civil agreement covers situations where both parties have taken independent legal advice.