What is shader in Unity 3d and can I eat it?

As we all know, Unity3d is a very wide cross-platform game engine, easy to start, user-friendly interface, integration features are many, is currently developing hand-tour of the mainstream engine. I had the privilege of using unity 3d to develop for more than a year and had a glimpse of the power of this arrivals engine.

Writing shader is also part of my work, first of all, to say what shader is, I explained with my own understanding:

First, shader is a language, a high-level language that executes on the GPU, which is the graphics card. Shader is intended to be a shader that can customize two links in the GPU's rendering pipeline (that is, vertices and fragments). As a result, we can control the rendering of objects on the screen, and even achieve some very powerful effects.

What is shader in Unity 3d and can I eat it?