“Opaque Translucency” is essentially a translucent material that is full opacity, but uses the scene texture for plugged into the emissive so that it looks translucent.
The most common use for this is for blurred glass, because you can blur the scene texture. But by using fresnel and a cubemap you can also blend reflections into it, allowing you to get glass that kinda looks like it is using lit translucency at a 10th of the cost by using the unlit shader.