Loans where the borrowers' down payment is less than 20% often require mortgage insurance, which can be provided privately or publicly.
Conventional loans requiring MI first instance of mortgage insurance are insured by private mortgage insurance. FHA loans are those whose MI is provided by the Federal Housing Administration, a public, government program backed by taxpayers.
Both mortgage insurance options have premiums, often paid by the borrower. Each program has advantages and disadvantages depending on your unique situation.