Toggle switch is the simplest form of switch, operated by a toggle lever that can be pressed up and down. According to the convention, position of the lever downwards to indicate OFF conditions or switch contacts is disconnected, and position of the lever upwards to indicate ON conditions or switch contacts are connected.
Toggle switch have two terminal tag, which indicates that switch have a contact type single pole single throw or single pole single direction, which is usually referred to as SPST switch.
Toggle switch that are smaller have three terminals tag, which indicates that switch have a contact type single pole double throw or single pole two direction, normally abbreviated with the SPDT switch. Terminal tag at the center is the line common current flow and can establish contact with either of these two other tag. Such contacts are called changeover contacts switch.
Symbol for SPST switch and SPDT switch as shown below