Define temperature coefficient of resistance.

‘Temperature coefficient of resistance is defined as the ratio of change in resistance of a conductor to its original resistance per 1°C rise in its temperature (or)
Temperature coefficent of resistance ($\mathrm{\alpha }$) is defined as the fractional change in resistance per unit change in temperature $\mathrm{\alpha }=\frac{\mathrm{\Delta R}}{\mathrm{R\Delta t}}{/}^0\mathrm{C}$.