A security that represents part ownership of a company is called a(n) ________________.

A security that represents part ownership of a company is referred to as "stock." When individuals purchase stock, they acquire shares of the company, which entitles them to a portion of the company's profits and assets, as well as voting rights in certain corporate decisions. Stocks are a fundamental component of the equity markets and serve as a way for companies to raise capital by selling ownership stakes to investors.

In contrast, a certificate of deposit is a time deposit offered by banks with a fixed interest rate, a bond represents a loan made by an investor to a borrower (typically a corporation or government), and an annuity is a financial product that pays out a fixed stream of income over a specified time period, usually used for retirement planning. Each of these options serves a different financial purpose and does not convey ownership in a company like stock does.