Deduction

In accounting, any item or expense that the tax code allows a person or organization to subtract from the cumulative taxable revenue total is considered a "deduction."

Akin to a credit, it is essentially an extra bookkeeping entry that results in extra money kept and not paid to the the TaxMan. The entire accounting profession becomes more lucrative the greater the expertise at applying deductions that will hold up and thwart confiscatory tax policies that would otherwise be in effect.