Metallic luster refers to the way light casts off of a mineral. Polished metals such as gold have a metallic luster, which makes them look bright and shiny, and reflect more light than other minerals. There are also minerals that have metallic luster, but are not shiny or reflect much light, which is called dull metallic luster.
Metallic luster - bright, shiny
Dull metallic luster - not shiny