Which term refers to the mixture of debt and equity used to finance a firm?

The correct term that refers to the mixture of debt and equity used to finance a firm is capital structure. Capital structure is a fundamental concept in finance that outlines the proportion of debt (loans and bonds) and equity (stocks and retained earnings) that a company uses to fund its overall operations and growth. This balance is crucial because it affects the company’s risk and return profile, influencing both operational decisions and valuations.

Understanding capital structure is essential for managers as it determines how a firm raises capital and the cost of that capital. A well-defined capital structure can optimize the firm's financial performance and minimize the cost of financing. It also plays a significant role in how external stakeholders perceive the firm’s financial stability and risk.

The other options do not accurately define the mixture of debt and equity. Financial leverage pertains specifically to the use of debt to increase potential returns but does not encompass the full structure of financing. An investment portfolio refers to a collection of assets held by an individual or institution, typically for investment purposes, instead of describing how a firm is financed. A revenue stream denotes the source of revenues for a business, indicating how income is generated rather than how financing is arranged. Therefore, capital structure is the most accurate term for describing a firm's financing mix.