A Treasury bill (or T-Bill) is a short-term government debt security, which yields no interest. Rather, it is issued at a discount on the redemption price.
Basically, the Federal Government issues treasury bills at discounted prices for maturity periods 91, 182, and 364 days. At the end of the selected maturity period, the government buys the bills back at full price. For example, let’s say you buy an 182-day ₦200,000 treasury bill at a discounted rate of ₦180,000. The Federal Government of Nigeria writes an IOU for ₦200,000 and agrees to pay it back in 182 days.