If you have a dual battery system installed in your vehicle, or if you are towing a caravan or camper trailer, you may need an Anderson plug. In short, an Anderson plug is a special power connector used to connect high current circuit devices.
A battery connector is something that allows current to pass through this part to a given part, it can only carry current (AC and DC), not information flow.
Anderson connectors are not really waterproof, but there are some waterproof fittings available to prevent shorting of wires due to moisture.