Pole:
Describes the number of circuits that the switch will activate simultaneously.

Single Pole: 1 circuit (will have spade connectors on one side of the back of switch).
Double Pole: 2 circuits (will have spade connectors on both sides of the back of switch).

Throw:
Describes the number of positions on the switch that activate circuits.

Single Throw: 1 position when switched from the "off" position.
Double Throw: 2 positions when switched from the "off" position (center position is off).

Momentary / Sustained Contact:
Circuits such as lighting and windshield wipers require continuous current for continuous operation, and require switches with Sustained Contacts. When the actuator in this type of switch is at the "on" position, it will stay until moved to the "off" position

Circuits for a horn or engine trim require current only when the switch is held to complete the circuit, and require switches with Momentary Contacts. When your finger is removed from the switch, spring action in the switch will move the actuator back to the off position.