Why was Esau called Edom in the Bible?

According to research, the Hebrew word Edom means "red", and the Hebrew Bible links it to the name of its founder, Esau, the eldest son of the Hebrew patriarch Isaac, because he was born "red all over" (the red color was used to describe the color of the hairs of Esau). As a young adult, he sold his birthright to his brother Jacob for a “red pottage”. The Tanakh describes the Edomites as descendants of Esau.