First, the definition of the birthright. The birthright, which is sometimes called the primogeniture, is the right of inheritance normally accorded in olden times to the firstborn male in the family. A number of things were involved in birthrights. These things varied according to whose birthright it was, that is, what the situation was of the family involved, as we will see next. Second, the description of the birthright. The birthright before us which Esau sold to Jacob was a very special birthright.