The passengers' weight (but not the driver's) is included in the car's maximum permitted load. This means that you are probably not allowed to transport a lot of load if you have several passengers in the car.
The maximum load is the car or trailer's maximum permitted load according to the registration certificates.
Car's kerb weight: The weight of the car with the driver when it is unloaded and fully equipped (with tools, spare wheel, fuel, engine oil and water).
Trailer's kerb weight: The weight of the trailer when it is unloaded.
Gross weight: The actual weight of the car or the trailer at a certain moment. This means the gross weight varies depending on load and equipment.
Maximum load: The car or trailer's maximum permitted load according to the registration certificates.
Total weight: Kerb weight + maximum load.