An estate in expectancy is either a reversion or a future estate.
D.C. Code § 42-508
Estate in expectancy
Mar. 3, 1901, 31 Stat. 1351, ch. 854, § 1018
Official source: D.C. Law Library (Council of the District of Columbia). Reproduced from public-domain District of Columbia statutes; confirm against the official source for the current text. Not legal advice.