What does it mean when it says "This note is legal tender For all debts, public and private"?

Question

I was looking at this $5 bill and I wondered what the "Private" part of debts meant, any ideas?

Answer 1

If i owe you money , i can pay you with this and our debt is legally settled.  In the old days,  no one knew who had printed what.  They only trusted gold and silver, not a piece of worthless paper.

Answer 2

There are two types of debt.   Public debt is better known today as government debt.  That is what the government owes.  

Private debt is all other debt.  What you owe a business; what one business owes another business; or what one individual owes another individual.

Answer 3

If I owed money to you, or you to me.

Between you and me is private.

Answer 4

Personal debts between friends and associates.