When a year has 366 days instead of 365 days it is known as leap year. We say there are 365 days in the year and by this we mean that it takes the earth 365 days to make its annual trip around the sun. Actually, though, It takes the earth 365-1/4 days to make this trip. This means that every year we gain one-fourth of a day and every four years we gain one full day. If we did nothing about this, our calendar would move backward one full day every four years to keep this from happening, we add the extra day every four years and put it into February.