Mortgage Backed Securities
When you take out an interest only mortgage you don’t pay any of the capital back until the end of term (which in this case is 10 years) and so every year you pay back the interest on the $1m that you borrow which is $100k.
This means you pay back $100k every year for the 10 years but then at the end of the term you still need to pay the amount you originally borrowed so the payment in year 10 is $1m + $100k. Hope this helps.