Wiktionary
tax shield
n. The reduction in income taxes that results from taking an allowable deduction from taxable income.
Wikipedia
Tax shield
A tax shield is the reduction in income taxes that results from taking an allowable deduction from taxable income. For example, because interest on debt is a tax-deductible expense, taking on debt creates a tax shield. Since a tax shield is a way to save cash flows, it increases the value of the business, and it is an important aspect of business valuation.