Generally, a transferable instrument representing an ownership interest in a corporation (equity security or stock) or the debt of a corporation, municipality, or sovereign. Other forms of debt such as mortgages can be converted into securities. Certain derivatives on securities (e.g., options on equity securities) are also considered securities for the purposes of the securities laws. Security Futures Products are considered to be both securities and futures products. Futures contracts on Broad-Based Securities Indexes are not considered securities.

Source: Commodity Futures Trading Commission