A surd is a root (e.g. $\sqrt{n}$, $\sqrt{3}$, $\sqrt{17}$ and $7\sqrt{2}$).

Surds are irrational numbers because they cannot be expressed as a fraction $\dfrac{a}{b}$.

They are non-recurring decimals, e.g. $\sqrt{3}=1.732050807568877...$

Surds can be simplified by factoring out perfect squares.