I talked about real life. CG only try simulate this.
All materials have holes, and light pass inside this holes or can not pass, because particules too closely.
If you decrease thickness of a paper, then paper can pass too much light. Or you increase particule interval, paper can pass too much light, etc, etc.
Translucency = Light scatter inside the material? Yes. Then we say Translucent.
Diffuse = Light scatter outside the material? Yes. Then we say Diffuse.
SSS = Light scatter inside the material? Yes. Light scatter only one direction? No. Then we say “Subsurface Scattering”. SSS also translucency, but have multi direction, not one direction.
Transparency = Light pass inside the material without scatter? Yes. Then we say Transparent. And in real life, all light rays never pass with scatter. Some rays not scatter, some rays too low scatter.
Light pass (one direction, not transmission) based on the material thickness and particle interval.
When we try simulate this phenomenons, we must decide how I simulate this effects.