A brass instrument is defined as an “aerophone,” which means it is an instrument where the musician must blow air into the instrument. The musician produces the tone by buzzing their lips into what is generally a cup-shaped mouthpiece. It doesn’t mean that the instrument is necessarily made of brass, since some instruments that are made of other metals like wood, horn, or even animal bone are included in the family of brass instruments. Other instruments that are made of brass or metals such as the flute or saxophone are not brass instruments.