What is Back Taxes?

Legal Definition
Back taxes is a term for taxes that were not paid when due. They are typically taxes that are owed from a prior year.
-- Wikipedia
Legal Definition
Those taxes assessed for a previous year or years and remaining due and unpaid from the original tax debtor. M. E. Church v. New Orleans, 107 La. 611, 32 South. 101; Gaines v. Galbraeth, 14 Lea (Tenn) 363.
-- Black's Law Dictionary