Shiny Metal is one of the base metals added by Thermal Foundation. It is also the rarest of the base metals. It can be obtained from Shiny Ore and, less commonly, Ferrous Ore.
Shiny Ore and Ferrous Ore can also be processed in various ways in an Induction Smelter, with varying byproducts.
Like most base metals in the mod, Shiny Metal can be used to craft tools and armor. Other than that, it does not serve much purpose, besides being a critical component in creating the powerful alloy Enderium.
The reason the metal is not called Platinum is because it is not part of the seven metals of antiquity. In the setting of the game, the modern name of the metal wouldn't have been defined yet. This results in the player calling the metal Shiny Metal; a name that describes the metal rather than the modern scientific name.