Let $y= f \left(x\right)$ be a function defined on an interval $A$ and $x\in A$. Let $\delta x$ be any change in $x$ and $\delta y$ be the corresponding change in $y$. 

Then 

$\text{ (i) }\frac{\delta y}{y}$ is called relative error in $y$

$\text{ (ii) }\frac{\delta y}{y}\text{×100}$ is called percentage error in $y$.