Quoting from two book's here Book 1 "Shading is the term in Maya software for applying colours and textures, knows as shaders, after you model your objects... Shading is the proper term for applying a renderable colour, surface bumps etc, Texturing is formally used when applying a map.... The porcess of shading is often refered to as texturing A shader is a material node such as the Lambert, Blinn, Phong.." Book 2 " Texturing generall refers to the process of building a surfaces detail indicating how that surface will react to light.." I looks to me that there is a difference as Magicsy said but it appears that the terms are pretty much interchangable, depending who you talk too.