Answer: Flat shapes like squares, circles, and triangles are a part of flat geometry and are called 2D shapes. These shapes have only 2 dimensions, the length and the width. Examples of 2D shapes in flat geometry include circles, triangles, squares, and rectangles. Solid objects are also known as 3D objects having the third dimension of height or depth. Examples of 3D shapes in solid geometry include cubes, cuboids, spheres, and cones.