in the Old Testament of the Bible, the son of Isaac, and the older brother of Jacob, whose twin (=one of two children born at the same time) he was. Esau was very hungry and so he sold his birthright (=the property or possessions that he had a right to receive from his parents) to Jacob for "a mess of pottage", that is, for some soup that Jacob had made.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.