Bright tin and Matte tin are two types of tin plating that produce different finishes.
Bright tin produces a shiny and reflective finish that is mainly used for appearance. It is also aesthetically pleasing and will provide a slightly lower coefficient of friction when mating with the other half of the connector. Bright tin will also slightly reduce the insertion force.
Matte tin produces a matte finish with a dull, white surface that is mainly used for drawing applications. The matte tin coating is made in electrolytes without the addition of brighteners.