Why is a "quarter panel" called that? What is it a quarter of?

Answer 1

i belive it comes from the old days when that would have actually been one quarter of the body work of the car, and it has stuck since then.

Answer 2

quarter panel
On an automobile, a quarter panel is a body panel that covers the section between the door and the hood, or the door and the trunk. In some countries, for example the United Kingdom, the term is only used to refer to the rear panels. They are typically made of sheet metal, but are sometimes made of fibre-reinforced plastic. They are the parts of the exterior of the car that's left once the hood, trunk, roof, doors, bumpers, lights, and plastic trim are taken away. They typically wrap around the front and rear wheel wells. The quarter panels may or may not extend to cover parts of the A- or C-pillars.

Answer 3

Probably an old coach building term. There is a lot of tradition in body and coach work. I think it just means the rear quarter of the car front half and back half makes up four quarters. That is what I always thought. By the way the front two fenders and grill are called the "front clip" collectively. There is the hood, of course, and the trunk lid or bonnet. I have heard the trunk lid refered to as a "turtle."