The order of a surd is the number denoting the root. For example the orders of the surds \(\sqrt 3 ,\;\sqrt[3]{5},\;\sqrt[7]{{11}}\) are second, third and seventh. 

In the surd \(7\sqrt {11} \), 7 is called coefficient of the surd, 2 is order of the surd and 2 is radicand. When there is no coefficient in a surd, it is assumed that coefficient is 1. 

Similar Surds:

Two or more surds are said to be similar, when they can be so as the same irrational factor. Thus \(\sqrt {24} \) and \(\sqrt {54} \) are similar surds because they can be written as \(2\sqrt 6 \) and \(3\sqrt 6 \). They have same irrational factor\(\sqrt 6 \)