What is "unclaimed" imputed income?

That is income that the IRS believes you should have declared, but did not for personal reasons, usually due to the money being due from a family member.

Example: You lend your son $100,000 to buy a house, and he pays you back $10,000 per year over ten years with no interest. The IRS finds out about it and "imputes" the interest that you would have collected had you lent that money to a perfect stranger.