SPST: Single Pole, Single Throw switches control a single wire circuit with two positions OFF-ON

SPDT: Single Pole, Double Throw switches control two single wire circuits permitting only one circuit to be energized at a time. Can be two positions ON-ON or three positions ON-OFF-ON

DPST: Double Pole, Single Throw switches control two circuits simultaneously. Circuits are ON at the same time, and OFF at the same time.

DPDT: Double Pole, Double Throw switches control four circuits permitting only two circuits to be energized at a time. Can be two positions ON-ON or three positions ON-OFF-ON.