Built-in shader include files

HLSLSupport.cginc - (automatically included) Helper macros and definitions for cross-platform shader compilation.
UnityShaderVariables.cginc - (automatically included) Commonly used global variables.
UnityCG.cginc - commonly used helper functions.
AutoLight.cginc - lighting & shadowing functionality, e.g. surface shaders use this file internally.
Lighting.cginc - standard surface shader lighting models; automatically included when you’re writing surface shaders.
TerrainEngine.cginc - helper functions for Terrain & Vegetation shaders.

UnityCG.cginc

Data structures in UnityCG.cginc

struct appdata_base: vertex shader input with position, normal, one texture coordinate.
struct appdata_tan: vertex shader input with position, normal, tangent, one texture coordinate.
struct appdata_full: vertex shader input with position, normal, tangent, vertex color and two texture coordinates.
struct appdata_img: vertex shader input with position and one texture coordinate.