Jumbo Loans in this context are any mortgage which is not guaranteed or insured by the US Government which has a loan balance over the Conforming Loan Limit set by Fannie Mae and Freddie Mac.  Currently the conforming limit is $548,250 for a Single-Family unit with exceptions in Alaska and Hawaii.

Because of the larger loan amount the risk associated with the loan increases and therefore down payment requirements are usually set higher than other loans to mitigate that risk.  Jumbo loans also may have a higher interest rate compared to a similarly structured Conforming Loan.