In your case, this is equivalent to writing:
final double EPSILON = 0.00000000000001;
except you don't have to count the zeros. This is called scientific notation and is helpful when writing very large or very small numbers.
The "E" notation is scientific notation. You'll see it on calculators too. It means "one times (ten to the power of -14)".
For another example, 2E+6 == 2,000,000.
1E3 => 1000
1E-1 => 0.1
1E-2 => 0.01
It's a way for writing 1 * 10-14
That's Exponential notation
1E-14 is 1 times 10 to the power of -14