The radical symbol by itself is used in math to represent taking the square root of an expression. It is also used to represent taking the $n$throot of a number when a number is place above the start of the symbol. Typically the radical symbol is used in an expression like this:
$4 $
In plain language, this means take the square root of the number four. Shown below are various computer formats for the radical symbol.
Symbol  Format  Data 

√  Unicode 

√  TeX 

SVG 