The arrangement of two different metals (or semiconductors) joined at their ends to form a loop is called a thermocouple. Ends are called junctions. Temperature difference applied to a thermocouple creates a voltage in it & vice versa. This effect of direct conversion of temp. differences to electric voltage & voltage differences to temp. is called the thermoelectric effect or thermoelectricity.
Traditionally, the term thermoelectricity encompasses three separately identified effects, the Seebeck effect, the Peltier effect, and the Thomson effect. Peltier effect is due to the contact of different metals. Thomson effect is the absorption or evolution of heat along a non-uniformly heated conductor, Basic cause of thermoelectric effects is the diffusion of free electrons from the regions of high electron density to the regions of low electron density.