What is the Reason For Leap Day?

Growing up, I was always confused on why my cousin "Nat" only had an official birthday once every 4 years. "Nat" was born on a leap day. Granted he would celebrate his birthday on either the 28th or March 1st, technically it wasn't his birthday. But, I still can't wrap my head around why the random extra day shows up every 4 years.

Thankfully, one of the smartest people on the planet is here to help explain. Neil deGrasse Tyson explains Leap Year.