All shapes can be defined as the 2-dimensional/flat outlines of anything, so long that outline can start and end at the same place. Some shapes have definite man made names, while others are very unique and have no name at all. Shapes do not have volume and only have height and width.
In this picture of a round light, I see a round light with a shadowy background with a rectangle inside it. The shape can be seen in the circular look of the round light fixture. The round light fixture conveys a sense of completion and exact engineering since it is a complete circle. This image is appealing to me because it feels complete and whole.
In this picture of a Sand Dollar I see a Sand Dollar with a pattern of a star on a shell with several holes in it. The shape can be seen in the organic circle of the shell of the sand dollar. The Sand Dollar conveys a sense of elegance due to the pattern within the organic circle of the shell. This image is appealing to me because of the flower like pattern preserved within the Sand Dollar's shell