Treasury bill is a US Government Security, which is issued at a discount and matures at par in 4, 13, 26 or 52 weeks.
Applying "Treasury Bill" to Securities Exams:
The US Government will sell a variety of debt instruments to manage it cash needs. A Treasury bill’s maturity is shorter than a Treasury note and Treasury bond. As such the interest rate while not technically paid on the bill will be the lowest interest rate on Treasury securities.