Matte = non reflective, eg: paint comes in gloss, semi-gloss & matte.

Wiki:

A matte painting is a painted representation of a landscape, set, or distant location that allows filmmakers to create the illusion of an environment that would otherwise be too expensive or impossible to build or visit. Historically, matte painters and film technicians have used various techniques to combine a matte-painted image with live-action footage. At its best, depending on the skill levels of the artists and technicians, the effect is "seamless" and creates environments that would otherwise be impossible to film.