taxable period
(3) Taxable period The term “taxable period” means, with respect to an accumulated funding deficiency, CSEC accumulated funding deficiency, or unpaid minimum required contribution, whichever is applicable, the period beginning with the end of the plan year in which there is an accumulated funding deficiency, CSEC accumulated funding deficiency, or unpaid minimum required contribution, whichever is applicable, and ending on the earlier of— (A) the date of mailing of a notice of deficiency with respect to the tax imposed by subsection (a), or (B) the date on which the tax imposed by subsection (a) is assessed.