Translucency is a form of diffuse transmission where light passes through a thin object. This effect is often used to simulate things like leaves, paper, and thin plastics.
This parameter is the resulting color of the surface. You can choose a color or connect a texture or some other procedural pattern.
When light passes through a thin object, you may see shadows or silhouettes from the other side. Roughness can make the light from the other side appear to scatter more or be blurrier.
Here is where you supply a signal, either a texture or procedural pattern, to create a bump to the surface to "fake" surface details like small bumps or scratches. This means an artist doesn't have to model these tedious and often repetitious parts of a model.