All dates in Dynamics NAV have a corresponding closing date. A closing date is a period in time following the given date but before the next normal date. When you close an income statement using the Close Income Statement batch job Dynamics NAV creates a journal with closing dates. Typically this is a date between two months; C12/31/14 is for example after the last day in 2014 and before the first day in 2015. This is quite nice when you running your financial reports, which then enables you to do date filters to either exclude (01/01/14..12/31/14) or include (01/01/14..C12/31/14) the year end close transactions.