What is the function of an SPDT switch?

SPDT stands for 'Single Pole, Double Throw.' In switch terminology, the 'Pole' refers to the number of input circuits controlled by the switch, while the 'Throw' refers to the number of positions or output paths the switch can connect that input to. Because it is a 'Single Pole' switch, there is only one central input circuit. Because it is 'Double Throw,' this single input can be toggled back and forth to connect with one of two different output circuits. It acts exactly like a train track switch diverting a single train down one of two possible routes. Options describing multiple circuits being opened or closed simultaneously refer to Double Pole (DP) switches or basic Single Pole Single Throw (SPST) on/off switches. Only the SPDT fundamentally acts as a selector between two distinct paths.