The edge of a 3D shape is called an "edge." It is the line segment where two faces of the shape meet. In geometric terms, an edge is one of the fundamental components that define the structure of polyhedra and other solid figures.
edge
A 3D semi circle
A cone perhaps?
A cone.
it if called a edge for a 3D shape
edge
An edge.
A 3D semi circle
An impossible shape!
Cylinder
CONE
A cone perhaps?
A cone.
it if called a edge for a 3D shape
you call it a edge
2D shape = Decagon 3D shape = Decahedron
nonahedron