SUVs aren’t always four-wheel drive. Some SUVs operate on two-wheel drive, meaning the engine power is distributed solely to either the front two or back two wheels, and some operate on all-wheel drive. A 4x4 is any car that has power delivered to all 4 wheels.
There is plenty of crossover; many SUVs are 4x4, but not all. SUV is a term more commonly associated with the build and design of the car, rather than the number of driven wheels.
Four wheel drive is often the system of choice in vehicles used in more rural areas, particularly those that have to traverse more severe ground conditions. That’s because 4WD can be put in low power mode for all wheels to turn slowly, at the same time, making them perfectly paced to tackle snow or mud.
Those more suited to urban environments can allow an all-wheel drive car’s intelligent systems to decide the best way to distribute the car’s power.