In the general form of a surd, n√a,
a = radicand,
n = order of the surd,
the symbol √ used is called as radical,
and the whole expression
n√a is a surd.
So, in 5√4 ,
4 is the radicand,
5 is the order of the surd,
the symbol √ is radical and
5√4 is the surd.