A shader program, commonly referred to as a shader, is a program that runs on a GPU.
In Unity, shaders are divided into three broad categories. You use each category for different things, and work with them differently.
The terminology around shaders can be confusing; people commonly use the word “shader” to mean different things.
In this documentation, the terminology is as follows:
Shaderclass. A Shader object is a wrapper for shader programs and other information.
.shaderextension in your Unity project. It defines a Shader object.