Amortization is the schedule by which a loan's payments are applied to interest and principal over its term, so early payments cover mostly interest and later payments cover mostly principal, until the balance reaches zero. A seller carrying a note can set a longer amortization to lower the buyer's payment, paired with a balloon payment due sooner than the schedule would otherwise finish.
Why it matters
The amortization schedule tells you how much of each payment you are actually collecting versus lending back out.