A shader is what tells the renderer how to draw the surface, including what ti should do with any textures, and there aren't that many of them. A shader preset, which is what you probably mean, can set the material properties, and apply a shader other than the default, for any selected materials and it can, though ti doesn't have to, work with the already present textures. A materials preset does the same thing, but has a set of changes for specific, named materials rather than being applied to all seelcted materials.