What is Fee Tail?

Legal Definition
In English common law, fee tail or entail is a form of trust established by deed or settlement which restricts the sale or inheritance of an estate in real property and prevents the property from being sold, devised by will, or otherwise alienated by the tenant-in-possession, and instead causes it to pass automatically by operation of law to an heir pre-determined by the settlement deed. The term fee tail is from Medieval Latin feodum talliatum, which means "cut(-short) fee", and is in contrast to "fee simple" where no such restriction exists and where the possessor has an absolute title (although subject to the allodial title of the monarch) in the property which he can bequeath or otherwise dispose of as he wishes. Equivalent legal concepts exist or formerly existed in many other European countries and elsewhere.
-- Wikipedia
Legal Definition
A common law interest in land, now abolished in most states. The owner of land in fee tail isrequired to pass that land on to their children, who then may be required to pass it to their children. A fee tail is generally created when a deed uses the words "the heirs of his body," as in "to John Doe and the heirs of his body." In most jurisdictions in the United States, the fee tail has been abolished, and this language in a deed instead creates a fee simple.
Legal Definition
An estate tail; an estate of inheritance given to a man and the heirs of his body or limited to certain classes of particular heirs. It corresponds to the feudum talliatum of the feudal law, and the idea is believed to have been borrowed from the Roman law, where, by way of fidei commissa, lands might be entailed upon children and freedmen and their descendants, with restrictions as to alienation. 1 Washb. Real Prop. 66. For the varieties and special characteristics of this kind of estate, see Tail.
-- Black's Law Dictionary
Legal Definition
The estate of the donee of a conditional fee after the statute de donis. See 16 N. J. L. 181.
-- Ballentine's Law Dictionary