The document discusses the weighted average cost of capital (WACC). WACC incorporates the required rates of return of a firm's lenders and investors based on the mix of financing sources used, including debt, equity, and hybrid securities. WACC is important because it provides the minimum return a firm must earn to compensate its investors for the risk of its assets. Firms calculate WACC by weighting the cost of equity and the cost of debt by their respective proportions in the firm's target capital structure.