Numbers which cannot be expressed as p/q is known as irrational number.
Eg:- √2, √3, √5, π
Now,
√2 = 1.41421356...
√3 = 1.73205080...
√5 = 2.23606797...
π = 3.14159265...
We note that all the decimal expansion are non- terminating, non-repeating.