Some car manufacturers follow their own classification, they are classifying their cars for some marketing purpose, but usually these are the general difference between sedan and sports utility vehicle (SUV).
|Number of Boxes||Two or Three||Two|
|Purpose||On Road||On/Off Road|
|Cargo Compartment||Usually Separate, Shared with passenger compartment in some sedans||Shared with passenger compartment|
|Types||Notchback, Hatchback, Fastback, Hardtop||Mini, Compact, Mid-size, Full size, Extended.|
In Duster(SUV) there are only two compartments or boxes, Box 1 is for engine and its accessories, Box 2 is for passenger. Here there is no separate compartment for cargo as cargo compartment is shared with passenger compartment.
In Fluence(Sedan) there are three compartments or boxes. Box 1 is for engine and its accessories, Box 2 is for passenger, Box 3 is for cargo.
Image Source Renault India