Component only on editor

I try to understand one thing of the engine which is the only-editor component.
When you add a point light you have an icon in the editor which is a billboard component.
Since actor component is a parent-child hierarchy the billboard component is part of the hierarchy.
The renderer render each component of the parent-child hierarchy and the serializer of the engine will serialize each component.
I try to understand how the engine understand this component doesn’t have to be showed on the editor when selecting actor and doesn’t have to be serialized.
Can you light me up on that ?