Treasury bills are a type of short-term public debt issued by the Spanish Treasury.
Treasury bills are issued at auction and at a discount with a minimum amount of 1,000 euros. With a treasury bill, the government commits to repaying you the principal of your investment plus an agreed interest rate.
As they are issued at a discount, investors will pay, for example, 990 euros to receive 1,000 euros at the end of the agreed period.