Some facts are just things that we know, but never question. One of these things is that all of the months of the year have either 30 or 31 days, except for February. But what is up with that? And what is this leap-year thing?
Thousands of years ago, the calendar was created so that the Romans knew when to plant and harvest crops. Originally, the calendar had only 10 months and 355 days. Since the Romans believed even numbers to be unlucky, the days would either have 31 or 29 days. But when the days still did not add up to 355, they reluctantly decided to take another day from February, deciding it was an unlucky month. February was chosen as the odd month out because at that time it was at the end of the calendar.
Later, Augustus Caesar reorganized the calendar once again, adding 10 days. However, February still was left as a short month. Some say that this is because he gave an extra day to his favorite month, August. But the truth is actually just because in the original calendar, neither January or February even existed. So since the month was an afterthought, it was left as being the only one that is short.
As for leap years, these too were added due to incomplete accuracy of the calendar system. Obviously, the Earth does not take exactly 365 days to orbit the sun. Scientists eventually discovered that it took more like 365 and one fourth days. So every 4th year, and extra days is added to February to make up for this scientific accuracy.