Definition of proceeding clarifies scope of tax proceedings including past, pending and future matters under income tax law. The definition of proceeding for income tax purposes covers any tax proceeding in respect of any year that is pending when investigatory powers are invoked, any proceeding completed on or before that date, and any proceedings that may be commenced thereafter in respect of any year, thereby extending the scope of search and inspection powers to past, present and future tax proceedings tied to the same subject matter.