Gross Vehicle WeightThe combined weight of the automobile (Curb Weight), plus liquids, passengers, cargo, and, when towing an RV, the RVs tongue weight.Note: When towing an RV, the entire weight of the trailer is not considered to be part of the automobiles Gross Vehicle Weight, but the tongue weight is part of the automobiles Gross Vehicle Weight.
Tongue WeightThe weight placed on the hitch when the trailer is coupled to your vehicle. The tongue weight should be 10-15% of the RVs gross vehicle weight.Gross Vehicle Weight RatingThe maximum allowable weight of your vehicle. The Gross Vehicle Weight, which includes the Tongue Weight of the attached RV, should not exceed your vehicles Gross Vehicle Weight Rating.Tow RatingThe manufacturers rating of the maximum weight limit that can safely be towed by your specific vehicle. Weight is calculated by adding the RVs Gross Vehicle Weight with the weights of passengers, liquids or cargo in your vehicle.Gross Combination Weight RatingGenerally, the manufacturers rating of the maximum gross weight limit of the loaded tow vehicle combined with the attached RV. Important: When using max towing capacity to determine which RVs your vehicle can safely tow, remember that passenger weight, optional equipment, and additional cargo needs to be added into the equation. Do not exceed your vehicles towing capacity because doing so can affect your vehicles stopping ability, handling, or possibly even damage the drivetrain. You should always obtain your tow vehicles trailer weight and trailer weight rating from the appropriate manufacturer before purchasing or towing a trailer and you are responsible for your purchase and operation of your tow vehicle and/or trailer. Source - http://www.trailerlife.com/trailer-towing-guides/