The set of irrational numbers is formed by all numbers that cannot be expressed as the ratio between two integers.
2,3,5,e,π
Irrational numbers are real numbers, but they cannot be expressed as fractions. Also, the decimal expansion of irrational numbers is not repeating and non-terminating.
2π=1.41421356237…=3.14159265359…
In other words, a number is irrational if it is not rational. Although this number set does not have its own symbol, it is sometimes represented with a combination of other symbols.