GVWR
The maximum a single vehicle may weigh fully loaded, defined at 49 CFR § 571.3. It is a limit on that vehicle alone, not on vehicle plus trailer.
In practice
GVWR is a ceiling on one vehicle, set by the manufacturer and printed on the door-jamb label — not a measurement of what the vehicle currently weighs. It covers the vehicle, everyone in it, the fuel, the cargo, and the tongue weight pressing down on the hitch. That last inclusion is where people come unstuck: a trailer within your tow rating can still push the tow vehicle over its GVWR through tongue weight alone.
It is defined federally at 49 CFR § 571.3, which is why the term appears identically across manufacturers rather than meaning different things brand to brand. If you only ever check one number before hitching up, check the door-jamb label rather than a brochure: the label reflects the configuration your vehicle actually left the factory in, including options that add weight and subtract payload.