What is the difference between "Shader" and "Material"? I know that Shader is a type of computer program that used for shading. And it looks like Material also define how model looks like. That means for me, that in Blender "Material" equal "Shader" (or not?) But if it so, why same thing named differently in different parts of interface: 

 


Is there a some inconsistency here, or this is a different things? Can I call it "Material nodes" and "Shader tab" or it will be wrong?
Answer from Brecht Van Lommel:


  In Blender terminology material, light and world are datablocks that
  contain two things:
  
  
  Shaders to describe the look.
  Settings to control the quality.
  
  
  Shaders can be mixed, grouped, and shared between datablocks.
  
  The reason it’s not called the material editor is because you can also
  edit world, light and freestyle shaders there.


So materials define how object looks like, and have some additional material-specific settings. Shaders define object materials and also lights, world and freestyle as a part of each data-block.