Definition of Executory Interests
A general term, comprising all future estates and interests in land or personality, other than reversions and remainders.
A contingent future interest which: (a) cannot qualify as a remainder; (b) is always in favor of a conveyee, and; (c) takes effect when the contingency happens as a springing use or shifting use under the Statute of Uses (1535), or Statute of Wills (1540).
That's the definition of Executory Interests in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.