I understand a bit about leap year. This year for example is a leap year. 2012 has 366 days because it is a leap year. February has also 29 days and 29 is called a leap day. I remember a former colleague at the bank where I worked before, she celebrates her birthday every 29th of February. Does it means that she only gets a year older every four years? I guess you know what I mean with this one. But of course she gets older every year. The only thing is, she don't have her exact birth date when it is not a leap year.
This is how wikipedia explains leap year.
"A leap year (or intercalary or bissextile year) is a year containing one additional day (or, in the case of lunisolar calendars, a month) in order to keep the calendar year synchronized with the astronomical or seasonal year. Because seasons and astronomical events do not repeat in a whole number of days, a calendar that had the same number of days in each year would, over time, drift with respect to the event it was supposed to track. By occasionally inserting (or intercalating) an additional day or month into the year, the drift can be corrected. A year that is not a leap year is called a common year."