Any mortgage not insured or guaranteed by a government agency (FHA, VA, USDA).
Conventional loans are the most common type of mortgage. They're issued by private lenders and may be conforming (meeting Fannie/Freddie limits) or jumbo (exceeding them).
Conventional loans typically require higher credit scores (620+) and larger down payments (3-20%) than government-backed loans, but offer more flexibility in terms and don't require upfront funding fees.
PMI is required on conventional loans with less than 20% down, but can be canceled once the loan-to-value ratio reaches 80%.