Are they the ten that formed the Northern Kingdom of Israel, everyone except Judah and Benjamin, and were later scattered?
Are they the ones we don't really know where their descendants are (from patriarchal blessings, actual genealogy, etc.)? Everyone except Ephraim and Judah?
Are they the tribes that are neither Reuben (lost his birthright) nor Levi (birthright became temple service)?
Or are they ones we don't have records of, everyone except Judah (Bible) and Manasseh (Book of Mormon)?
Or are they the people who don't believe in Christ because "true believers in Christ, regardless of their lineage or geographical location" are of the House of Israel? (Bible Dictionary)
Try asking this question in Sunday School. It becomes a mess of theories.
