δOCF is a googological system introduced by a Japanese Googologist Jason, and is the first system defined by shifting definition. It was used to create a large number グラハム数〜legend of δ〜 submitted to a Japanese googology event as a variant of Graham's number, but was rejected by a referee because of the incompleteness of the definition. Namely, it is currently ill-defined.
It is intended to perform as an ordinal function associated to an OCF through the method. Although it is currently ill-defined, it is expected to be a powerful function which goes beyond many other OCFs if it will be appropriately formalised. Since it is quite complicated for others to understand from the explanation of its intended behaviour, Jason created δφ as a simpler ordinal function without using an OCF.