"It's a transcendental number"

A transcendental number is a number, that could be complex, but which is not algebraic and is also irrational. This means that the number cannot be a solution of a mathematical formula that features addition, subtraction and multiplication with rational or whole numbers in the calculations. Transcendental numbers cannot be represented as a formula, and instead are represented by symbols. Pi is a good example of this, as it is not the solution of any calculation, and is also not a whole number. In decimal terms, it is represented as 3.14159 26535 89793 23846 26433 83279 50288... and in symbolic terms π. It is difficult to understand this term if you don't have a mathematical background as it is!

Wikipedia

Wolfram MathWorld