Final answer:
Treasury Bills are a money market security, distinguishable by their short-term maturities and high liquidity, offering a safe investment backed by the U.S. government's credit.
Step-by-step explanation:
Among the options provided, Treasury Bills (T-bills) are considered a money market security. Money market securities are short-term debt instruments, typically with maturities of less than one year, used by governments and corporations to raise funds. Treasury bills, in particular, are short-term loans to the federal government with maturities of 13, 26, or 52 weeks and a minimum denomination of $10,000. Unlike stocks, which represent equity in a company, or bonds and mutual funds, which can be part of the capital market with maturities of more than one year, T-bills fall into the money market category due to their short-term nature and high liquidity.
T-bills are regarded as very safe investments since the only collateral required is the faith and credit of the U.S. government. They are included in the M2 money supply, along with savings deposits, money market funds, and certificates of deposit, highlighting their role in the financial system.