A Baloon payment on a Mortgage is a very large payment that is due at a certain point in the future.
Often the loan will be amortized over 15 years or 30 years but you must pay the balance of the loan after 5 years or 10 years. These loans are fairly common if someone has just come out of a divorce and does not have good enough credit to get a conventional loan. The 5 years until the balloon will give the person enough time to get their credit rating straightened around so they can get a conventional loan.
For instance on the first house I purchased in 1983 bank mortgage interest rates were very high (14% or higher as I recall). I bought the house and the owner of the house gave me a mortgage at 10% with a 30 year amortization but with a balloon payment due in 5 years. She wanted the loan to be paid off within 5 years. This worked out very well as in 5 years interest rates had come down and I traded the house on another property.