A fiscal year is an accounting term used to indicate the accounting period that is considered to be the "year" for a business entity. If the fiscal year begins on June 1st, this means that the accounting year is from June through May. The End of the Year Closing program should be run at the end of the fiscal year. There is no need to close at the end of the calendar year unless your fiscal year is also January through December.
This system keeps all donor and vendor records on a calendar year basis regardless of the fiscal year. That is January through December.