Equity

Equity is ownership: a claim on an asset after all debts against it are subtracted. For a public company, equity is its stock; for a homeowner, it is the home's value minus the remaining mortgage; on a balance sheet, shareholders' equity is total assets minus total liabilities.

The word does double duty in markets, referring both to the asset class ("equities" as shorthand for stocks generally) and to the specific ownership stake in a single company, which is worth keeping straight since both usages appear constantly in financial media.