4 terms

Future Interest

A future interest created in a grantee that's capable of becoming possessory upon the expiration of a prior possessory estate created in the same conveyance in which the remainder is created
Remainder is contingent
Either created in an unascertainable person or is subject to a yet aren't met condition precedent, or both.
Vested remainder subject to open
A remainder is vested in a group of takers, at least 1 of whom is qualified to take. But each class member's share is subject to diminution because additional taker (not ascertainable) can still join in.--class closes whenever any member can demand possession.
Executory interest
A future interest created in a transferee (3rd party) which is not a remainder and which takes effect by either cutting short some interest in another person (shifting) or in the grantor or his heirs (springing).