This document discusses the concepts of debt, equity, and debt-to-equity ratio. It explains debt as fees paid to teachers for their knowledge and guidance, similar to the debts companies take from banks. Equity is compared to the contributions of parents, who do not charge fees but see their children's success as their returns, just as company investors' returns come from profits. The debt-to-equity ratio measures a company's debt obligations relative to equity investments, with higher ratios indicating more debt and risk.