Definition of a radical number

[Hayker]

I would love to know the definition of a radical number...JUST a radical number. I'm terrible at memorizing anything and have completely forgotton this term. I don't want any other inormation then what I am asking. All I want is a few sentences to explain a radical number. Equations are the easy part of math.

 

[HallsofIvy]

A radical number (also called a 'surd') is any number that can be written as a root of a rational number or an algebraic combination of such.

Examples:
$\sqrt{2}$ is a "radical" number.

$^3\sqrt{7- \sqrt{3}}$ is a "radical" number.