Fiscal period
'fiscal period' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for year that I've seen before include "Manage" , "One-tenth of a decade" , "Period of 5 across" , "See 9" , "See 19" .)
(Other definitions for tax year that I've seen before include "I start in spring" , "It runs in the UK from the beginning of April" , "I finish on 5/4" .)