A more thorough explanation:

Definition: Cross-remainder is a future interest that arises when particular estates are given to two or more people in different parcels of land or in the same land in undivided shares, and the remainders of all the estates are made to vest in the survivor or survivors. Each tenant in common has a reciprocal, or cross, remainder in the share of the others. If no tenants or issue survive, the remainder vests in a third party (sometimes known as the ulterior remainderman).

Example 1: "To A and B for life, with the remainder to the survivor and her heirs."

Example 2: "Blackacre to A and Whiteacre to B, with the remainder of A's estate to B on A's failure of issue, and the remainder of B's estate to A on B's failure of issue."

Example 1 illustrates cross-remainder where two people, A and B, are given a life estate, and the remainder is given to the survivor. Example 2 illustrates cross-remainder where two people, A and B, are given different parcels of land, and the remainder of each estate is given to the other person on their failure of issue.

Cross-remainder is a complex legal concept that involves the vesting of future interests in multiple parties. It is important to consult with a legal professional to fully understand the implications of cross-remainder in a specific situation.