Is there any difference between "back door" and "rear door?"
I think there is a difference. Consider a car. You will certainly have front doors, where the driver and front seat passenger enter. You could have back doors, where the back seat passengers enter. Then you could have a rear door, where you put your cargo.
Talking about a car I would say front and rear doors. For a house I would say front door and back door.
In most cases, it is a hatchback. But my car literally has a 5th door. I would call it the rear.
Yes, it conveniently opens to the curb -- if you drive on the wrong side of the road.