This is a "cove", a sheltered inlet where land meets water. It's indented / concave shape is obvious.
In automotive terms, the 'cove panel' was a widespread stylistic treatment found at the rear of a vehicle. While other locations have also been termed the same (the '56-62 Corvette's side scoop comes readily to mind), I would like to focus on the rear of vehicles. Part of the reason for that is; at one point the rear of vehicles got as much design attention as the front, roughly the mid '50s into the late '60s. But that standard fell by the wayside, and most modern cars wear quite bland rears.
Like the geographical feature, the automotive cove panel would be a framed / concave section of the bodywork. One example would be the groundbreaking '65 Corvair :
To further define the treatment, I'd like to focus on painted cove panels. From a production standpoint, it took at extra assembly step to mask off and paint a secondary color in such a relatively small area. The above Corvair was the Corsa trim [either quad carbs or turbocharged], the other trim 'Vairs had the same cove but painted body color.
Of course the sheet metal as struck for the body allows the paint contrast, but while a number of cars had a similar feature they seldom offered it contrast painted. That extra step added flair and interest, and usually marked specialty models.