UnityCACAO-HDRP17/com.unity.render-pipelines.high-definition/Documentation~/snippets/shader-graph-blocks/smoothness.md

Smoothness The material's smoothness. Every light ray that hits a smooth surface bounces off at predictable and consistent angles. For a perfectly smooth surface that reflects light like a mirror, set this to a value of 1. Less smooth surfaces reflect light over a wider range of angles (because the light hits the bumps in the microsurface), so the reflections have less detail and spread across the surface in a more diffused pattern. None 0.5