Definitions for "equity security"
An instrument that signifies an ownership position (called equity) in a corporation,...
An equity security is defined broadly in Section 3(a)(11) to include a STOCK or similar SECURITY; or any security that is convertible, with or without consideration, into such a security or carrying any WARRANT or right to subscribe to or purchase such a security; or any such warrant or right.
Technically, all securities other than debt, although it may be used to denote common stocks alone, or preferred stocks that behave like common stocks.