Answer
The term $i$ is an imaginary unit which is the solution of the equation ${{x}^{2}}=-1$ and its value is $\sqrt{-1}$.
Work Step by Step
The term is an imaginary unit.
The imaginary unit $i$ is the solution of the equation,
${{x}^{2}}=-1$
The square root property is such that if ${{x}^{2}}=k$, then $x=\pm \sqrt{k}$.
$x=\pm \sqrt{-1}$
The solution of the equation is $\sqrt{-1}$ and $-\sqrt{-1}$.
The solution $\sqrt{-1}$ is called an imaginary unit $i$.
$i=\sqrt{-1}\text{ or }{{i}^{2}}=-1$
It expresses the imaginary number or a complex number which is in the form of $a+bi$.
Therefore, the term $i$ is an imaginary unit which is the solution of the equation ${{x}^{2}}=-1$ and its value is $\sqrt{-1}$.
