It is possible that different people will have different answers for this. March 14, 2015 could be special to different people for different reasons. However, I believe that the most likely answer to this question has to do with the mathematical constant pi. Pi is the ratio of a circle’s circumference to its diameter. The value of pi is generally given as 3.14 but it is an irrational number, which means that it never has a terminating or repeating decimal. If we go a few digits further in the value of pi, we see why March 14, 2015 is a special day.
To some people in the United States, March 14 is known as “pi day.” This is because Americans give dates with the month first and then the day. This means that March 14 can be written as 3/14. This is similar to 3.14, so people call March 14 pi day.
While every year has a pi day, 2015’s pi day is special. The value of pi, taken to four decimal places, is 3.1415. If you write the date of March 14, 2015 out, you get 3/14/15. This is similar to 3.1415. There is only one day like this in every century. It will not be possible to write the date as 3/14/15 until 2115.
Because of this, March 14, 2015 is a special day to some people. It is the only day this century whose date is similar to the value of pi taken to four decimal points.
Pi is a mathematical number, and its first few digits are 3.1415.
March 14th 2015 is 3/14/15 so this year's Pi day actual corresponds to the number.