noun

• (art, photography) A decorative border around a picture used to inset and center the contents of a frame.
  "The image is a perfect square of 8 cm (with white matte border the total dimensions are 14 cm tall by 11 cm wide)."
• (film) A background, often painted or created with computers
  "Matte painting is a tool that filmmakers can use to create a scene that is impossible to achieve with conventional cinematographic means."
• (pyrometallurgy) The molten metal sulfide phases typically formed during smelting of copper, nickel, and other base metals.

adj

• (American spelling) Dull; not reflective of light.
  "Flat or matte paint allows a deep color expression on the walls while also hiding flaws that may be inherent on the painted surface."

verb

• (transitive) To produce a dull, lustreless surface on (metal).