The Thomson effect refers to the phenomenon where a temperature difference in a conductor causes a flow of electric current, resulting in a change in temperature. This effect occurs when an electric current passes through a material that has a temperature gradient, leading to heating or cooling at different points along the conductor. Discovered by Joseph John Thomson, the effect is significant in understanding thermoelectric materials and their applications. It plays a role in devices like thermoelectric generators and coolers, which convert temperature differences into electrical energy or use electricity to create a temperature difference.