1) The right of a feudal lord to the return of lands held by his vassal, or the holding of a serf, should either die with out lawful heirs or suffer outlawry.
(MEDIEV-L. Medieval Terms)
2) Reversion of property to feudal lord or Crown upon default of heir or upon conviction of treason or felony.
(Sayles, George O. The King’s Parliament of England, 144)
3) The reversion to a lord of a fief for default of heirs or the outlawry of the holders.
(Warren, W.L. Henry II, 633)
*term definitions retrieved from Netserf’s Medieval Glossary
From the text of the Magna Carta of 1215:
If a man holds lands of any `escheat’ such as the `honour’ of Wallingford, Nottingham, Boulogne, Lancaster, or of other `escheats’ in our hand that are baronies, at his death his heir shall give us only the `relief’ and service that he would have made to the baron, had the barony been in the baron’s hand. We will hold the `escheat’ in the same manner as the baron held it.