SPDT stands for Single Pole Double Throw. It comes with 6 pin. It has 2 states ON and ON. For instance if we have two devices a red LED and a blue LED then SPDT switch will turn ON red in one position and blue in other position. By making different connections of the pins the two ON states can be made of same polarity or opposite polarity. Hence, it will switch ON a different device in each position. Hence, it is also known as changeover switch. This switch has found applications in industry, etc.