Definitions for "Noble metals"
A rare and expensive group of metals that resist corrosion such as gold (Au), iridium (Ir), platinum (Pt), palladium (Pd), ruthenium (Ru), and rhodium (Rh), some of which may be found in catalytic converters.
precious metals that cannot be altered by air or water (silver, gold, platinum)
Metals which are non-reactive, inert or resistant to oxidation. Traditionally includes, gold, silver and copper.