Jews can be (1) descendants of Judah, one of the twelve sons of Jacob, (2) people of the ancient southern kingdom of Judah, or (3) people who practice the religion, lifestyles, and traditions of Judaism but may or may not be Jewish by birth. It has become customary to use the word Jew to refer to all the descendants of Jacob, but this is a mistake. It should be limited to those of the kingdom of Judah or, more especially today, those of the tribe of Judah and his associates.