Brass instruments have at least two distinctive characteristics in common.  They are: (1) the sound is initiated by the vibration of the player’s lips; and (2) the instruments themselves are constructed of brass (usually plated with silver or gold lacquer). The definition does not, of course, include instruments once made of wood and now made of metal (such as the flute), or instruments made of metal which employ reed mouthpieces (such as saxophones).

These facts are usually quite well known among young brass players. Beyond this, however, many secondary school band members (and, I suspect, quite a few more advanced musicians as well!) do not seem to have any real understanding of how the different brass instruments produce sound.  Even fewer have any clear conception of how variations in design can alter tone colour or throw up slightly different problems in performance.