Treasury Bill
Also called: T-bill, treasury bills, bill
A Treasury bill is short-term government debt of one year or less, sold at a discount and redeemed at face value, with no coupon in between. The gap between the two prices is the interest. T-bills are the closest thing to a risk-free asset in finance and are the practical proxy for the risk-free rate in most models. They're also the direct competitor to a savings account: when bill yields exceed deposit rates, cash quietly migrates.