Ephraim (אֶפְרַיִם) is the dual form of a word meaning fruitful, from the root parah (to be fruitful). Joseph named his second son Ephraim saying, God has made me fruitful in the land of my affliction (Genesis 41:52). Ephraim became the dominant tribe of the northern kingdom.
Ephraim received the greater blessing from Jacob though he was the younger son — God's election reversing human expectation. God's love for Ephraim is expressed with astonishing tenderness in Jeremiah 31:20: Is Ephraim my dear son?... my heart yearns for him. God's love pursues the wandering and calls them home — a portrait of the prodigal father's love.