A more thorough explanation:

Remainder Vested Subject to Open

Remainder Vested Subject to Open is a type of future interest in property that is given to a class of people whose numbers may change over time and is to be shared equally by each member of the class. The class must have at least one member, but more can be added over time. For example, "to A for life, and then equally to all of B's children."

This type of remainder is vested because it is given to an ascertained person and is not subject to a condition precedent. It is subject to open because the class of people who will receive the property is not yet fully determined and can change over time.

Other types of remainders include:

• Contingent Remainder: a remainder that is subject to a condition precedent or given to an unascertained person.
• Defeasible Remainder: a vested remainder that will be destroyed if a condition subsequent occurs.
• Indefeasible Remainder: a vested remainder that is not subject to a condition subsequent and the remainderman is certain to acquire a present interest sometime in the future and will be entitled to retain the interest permanently.
• Cross-Remainder: a future interest that results when particular estates are given to two or more persons 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.

The examples illustrate how Remainder Vested Subject to Open works. In the example "to A for life, and then equally to all of B's children," the remainder is vested because it is given to a group of people who are already ascertained (B's children). However, it is subject to open because the number of people who will receive the property is not yet fully determined and can change over time if more children are born to B.