The debt-service coverage ratio indicates the amount of cash flow available to meet annual interest and principal payments on debt. A ratio less than 1 would mean a negative cash flow. A ratio of less than 1, say 0.95, would mean that there is only enough net operating income to cover 95% of annual debt payments.
Financial leverage relates to the practice of using debt to finance investments. An unlevered firm does its financing by issuing common stock and has no debt on its books. A levered firm finances part of its operation with debt.