The number \( \frac{1}{3} \) is a rational number that can be expressed as the square root of it, \( \sqrt{\frac{1}{3}} \).
Since \( \sqrt{\frac{1}{3}} \) cannot be expressed as a fraction of two integers (it cannot be exactly represented as \( \frac{p}{q} \) where \( p \) and \( q \) are integers and \( q \neq 0 \)), it is classified as an irrational number.
Therefore, the correct response is:
irrational numbers