Suppose that 10 years ago you bought a home for $110,000, paying 10% as a down payment, and financing the rest at 8% interest for 30 years.
This year (10 years after you first took out the loan), you check your loan balance. Only part of your payments have been going to pay down the loan; the rest has been going towards interest. You see that you still have $86,848 left to pay on your loan. Your house is now valued at $170,000.
Your current situation
How much of the original loan have you paid off? (i.e, how much have you reduced the loan balance by? Keep in mind that interest is charged each month - it's not part of the loan balance.)