What does "birthright" mean?

Birthright: Any right, privilege, or possession to which a person is entitled by birth, such as an estate descendible by law to an heir, or civil liberty under a free constitution; esp. the rights or inheritance of the first born. Lest there be any . . . profane person, as Esau, who for one morsel of meat sold his birthright. Heb. xii. 16.