National Internal Revenue Code (NIRC)
Section 93. Definition of Deficiency. - As used in this Chapter, the term 'deficiency' means:
(a) The amount by which the tax imposed by this Chapter exceeds the amount shown as the tax by the executor, administrator or any of the heirs upon his return; but the amounts so shown on the return shall first be increased by the amounts previously assessed (or collected without assessment) as a deficiency and decreased by the amount previously abated, refunded or otherwise repaid in respect of such tax; or
(b) If no amount is shown as the tax by the executor, administrator or any of the heirs upon his return, or if no return is made by the executor, administrator, or any heir, then the amount by which the tax exceeds the amounts previously assessed (or collected without assessment) as a deficiency; but such amounts previously assessed or collected without assessment shall first be decreased by the amounts previously abated, refunded or otherwise repaid in respect of such tax.