2d shapes are circles, ellipses, polygons (triangles, quadrilaterals, pentagons, etc.), angles, other non polygon shapes (like when you draw a star and the lines cross over each other.
3d shapes are shapes with added depth, such as tetrahedron, pyramid, prism (such as a cube), sphere (a ball), cone, etc.
A camera is a 3D shape. A photograph is a 2D projection of a 3D shape onto a 2D shape.
A television set is a 3D shape. The image (picture) on the television screen is a 2D shape. 3D is when it has length, width, and height. 2D is only length and width.
A square is a 2-dimensional shape. It has four lines, all of the same length. The opposite lines are parallel. All four angles are 90 degrees each.
A piece of paper is 3D.
2d
2D.
a pyramid is a 3D shape :)
It's a 2D shape.
A sheet ( piece) of paper is a 3 - dimensional object. The length and width can be measured with a ruler. However, the thickness (3rd dimension) you will need a micrometer to measure the thickness. As a solid object it is a 'cuboid'.
3D
A nonagon is a 2D shape and there is not a 3D equivalent shape.
The suffix "hedron" implies 3D. The 2D suffix is "gon"