Gross Vehicle Weight Rating (GVWR): The total allowable weight for the vehicle, including occupants, fluids, options, hitch hardware, cargo and trailer-hitch weight.
Gross Combination Weight Rating (GCWR): The total allowable weight of the tow vehicle, the trailer, the cargo in each, hitch hardware, fluids and occupants. EVERYTHING.
Gross Axle Weight Rating (GAWR): The total allowable weight on an individual axle. This includes the weight of the tires, wheels, brakes and the axle itself.
Maximum Tow Rating: The manufacturer’s weight limit for towed loads. For conventional trailers, this normally includes a hitch-weight limit as well; for fifth-wheels, the pin weight is applied to the truck’s GVWR and its rearaxle GAWR
Unloaded Vehicle Weight (UVW): Weight for the trailer, unloaded
Hitch Weight Rating: Indicates the maximum weight your hitch is designed to safely carry.
Tongue Weight: The weight exerted on the hitch ball.
This is a useful site for definitions if you need more. We’ve spent a lot of time wrestling with these figures across different vehicles to figure out what we can, and what we want to be able to, tow. Initially we thought we’d be towing with our Volvo XC wagon, but we got some good advice from the first camper salesman we spoke with: don’t buy the camper to fit your current tow vehicle; buy the camper you want and upgrade your tow vehicle to fit IT. Not the most practical approach, I guess, but it makes sense when you think about the trailer being home for extended periods of time.