Don't understand

<script>
      var diameter = 5.75,
          a = 17,
          b = 42,
          c = 1337,
          ageIfILiveToYear2100 = (new Date(2100, 0, 1) - new Date(1995, 5, 16, 7, 20)) / (1000 * 60 * 60 * 24 * 365.242);

      /*
      The JavaScript Math object has the following
      constant (among others):
      Math.PI
          Approximately 3.14159. Pi (π) is used
          to determine the circumference of a circle
          given its diameter by multiplying the diameter
          by π. Geometery refresher: the circumference
          of a circle is the distance around the outside
          edge. The diameter is the width of the circle.

      The JavaScript Math object also has the following
      methods (among others):
      Math.random()
          Returns a random number between 0 and 1
      Math.max(a, b, ...)
          Returns the largest value of the passed
          arguments
      Math.floor(a)
          Returns the value of a number rounded down to
          the nearest integer
      */



    </script>