This page provides a table-oriented access to the Material parameters. A more WYSIWYG-like access is provided by page Assets/Materials/Editor which, however is restricted to the standard Phong parameters.
The page offers access to all Material parameters such as
The Shininess coefficient controls the specular highlights as defined in the original Phong lighting model. The value should be 1 or bigger. The bigger it is, the smaller is the size of the specular highlight. Shininess should be considered only if there's a specular color value.