Definition:Root (Analysis)

Let $$x \in \R$$ be a real number such that $$x > 0$$.

Let $$m \in \Z$$ be an integer such that $$m \ne 0$$.

Then there always exists a unique $y \in \R: y > 0$ such that $$y^m = x$$.

This $$y$$ is called the $$m$$th root of $$x$$, and is denoted $$y = \sqrt [m] x$$.

When $$m = 2$$, we write $$y = \sqrt x$$ and call $$y$$ the square root of $$x$$.

When $$m = 3$$, we write $$y = \sqrt [3] x$$ and call $$y$$ the cube root of $$x$$.

The $$m$$th root of $$x$$ can also be written, using the power notation, as $$x^{1/m}$$.

Note the special case where $$x = 0$$: $$\sqrt [m] 0 = 0$$.

Also see
Compare with Power.