Surface Shader output structures in the Built-In Render Pipeline

Important: The Built-In Render Pipeline is deprecated and will be made obsolete in a future release.
It remains supported, including bug fixes and maintenance, through the full Unity 6.7 LTS lifecycle.
For more information on migration, refer to Migrating from the Built-In Render Pipeline to the Universal Render Pipeline and Render pipeline feature comparison.

Standard output structure of surface shadersA program that runs on the GPU. More info
See in Glossary is this:

struct SurfaceOutput
{
    half3 Albedo;   // diffuse color
    half3 Normal;   // tangent space normal, if written
    half3 Emission;
    half Specular;  // specular power in 0..1 range
    half Gloss; // specular intensity
    half Alpha; // alpha for transparencies
};

In Unity 5, surface shadersA streamlined way of writing shaders for the Built-in Render Pipeline. More info
See in Glossary can also use physically based lighting models. Built-in Standard and StandardSpecular lighting models (see below) use these output structures respectively:

struct SurfaceOutputStandard
{
    half3 Albedo;       // base (diffuse or specular) color
    half3 Normal;       // tangent space normal, if written
    half3 Emission;
    half Metallic;      // 0=non-metal, 1=metal
    half Smoothness;    // 0=rough, 1=smooth
    half Occlusion;     // occlusion (default 1)
    half Alpha;     // alpha for transparencies
};
struct SurfaceOutputStandardSpecular
{
    half3 Albedo;       // diffuse color
    half3 Specular; // specular color
    half3 Normal;       // tangent space normal, if written
    half3 Emission;
    half Smoothness;    // 0=rough, 1=smooth
    half Occlusion;     // occlusion (default 1)
    half Alpha;     // alpha for transparencies
};

Introduction to surface shaders in the Built-In Render Pipeline

Surface Shaders and rendering paths in the Built-In Render Pipeline

Unity Manual

Surface Shader output structures in the Built-In Render Pipeline