prenuptial agreement

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A legal agreement made between persons intending to marry, establishing certain conditions of the marriage and its dissolution, especially as pertaining to the individual ownership of certain property that would otherwise be considered jointly owned marital property under state law.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun US a legal document, signed by both parties before marriage, stating the legal claims on each other's estate upon a subsequent divorce