Unity has two physics engines, one for 3D and one for 2D. When we use 2D physics engine a collider 2D component must be used. There are four collider 2D component. Each collider 2D component is optimesed for a particular shape.
The circle collider 2D : It works with round circular objects. The box collider 2D : It works with rectangular objects. The polygen collider 2D : It works best with complex shapes. The edge collider 2D : It works well for surfaces.
The edge collider and polygen collider are very similar, they are created by various points or vertices with edges connecting them but the main difference between them is that the polygen collider must be a closed shape covering an area and the edge collider must be open defining an edge of segments.