A balloon payment mortgage is a mortgage which does not fully amortize over the term of the note, thus leaving a balance due at maturity. The final payment is called a balloon payment because of its large size. Balloon payment mortgages are more common in commercial real estate than in residential real estate.
A balloon payment is a larger-than-usual one-time payment at the end of the loan term. If you have a mortgage with a balloon payment, your payments may be lower in the years before the balloon payment comes due, but you could owe a big amount at the end of the loan.