In leap years, it's the last day in February
The (usual) second part of February was incorporated in the 
intercalary month as its last five days, with no change either in their dates or the... [DOC] [TLE] Leap year - Wikipedia [PAR] A leap year is a year containing one additional day added to keep the calendar 
.... February 29 is a date that usually occurs every four years, and is ... named 
many of its days after the syzygies of the moon: the new ... in the last five days of 
February were moved to the last five days of Intercalaris.