Son of Joseph. “Before the year of famine came, Joseph had two sons, whom Asenath, the daughter of Potiphera priest of On, bore to him. Joseph called the name of the first-born Manasseh, ‘For,’ he said, ‘God has made me forget all my hardship and all my father’s house.’ The name of the second he called Ephraim, ‘For God has made me fruitful in the land of my affliction’” Gen 41:50–52.
Each tribe was given a separate territory in Canaan, except for the tribe of Levi, which was set apart to serve in the Tabernacle. Because Jacob-Israel adopted Joseph’s two sons, Ephraim and Manasseh, as his own and blessed them, Joseph’s territory was doubled. They became separate tribes with separate territories. “For the people of Joseph were two tribes, Manasseh and Ephraim; and no portion was given to the Levites in the land, but only cities to dwell in, with their pasture lands for their cattle and their substance” Josh 14:4. And so, based on their positions around the Tabernacle and on territory, the eastern tribes were Judah, Issachar and Zebulun. The southern tribes were Reuben, Simeon, and Gad. The western tribes were Ephraim, Manasseh, and Benjamin. And the northern tribes were Dan, Asher, and Naphtali.
After the tearing of Israel, Ephraim’s tribe merged with that of the northern kingdom, so the ten “lost tribes” of the northern kingdom were collectively called Ephraim, after its largest tribe.
“Say to them, ‘Thus says the Lord GOD: Behold, I am about to take the stick of Joseph (which is in the hand of Ephraim) and the tribes of Israel associated with him; and I will join with it the stick of Judah, and make them one stick, that they may be one in my hand’” Ezek 37:19.