base period
(4) Base period For purposes of this subsection— (A) In general The term “base period” means, with respect to any taxable year, the 5 taxable years preceding such taxable year. (B) New private foundations, etc. If an organization has not been a private foundation throughout the base period referred to in subparagraph (A), the base period shall consist of the taxable years during which such foundation has been in existence.