Your down payment is the cash you bring to closing toward the purchase price of the home. It's typically expressed as a percentage of the purchase price — a 10% down payment on a $400,000 home is $40,000.
Down payment minimums vary by loan program: 3% for some conventional first-time buyer programs, 3.5% for FHA, 5% for most conventional buyers, 10–20% for jumbo and second homes, 20–25% for investment properties, and 0% for VA and USDA.
A larger down payment reduces your loan amount, your monthly payment, and your PMI/MIP. But don't drain your savings to put more down — keep 3–6 months of housing expenses in reserves, and consider what else the cash could earn elsewhere.