This article does not have any sources. (January 2012)
With brass instruments, the sound starts at the lips. Their mouthpieces just help your lips buzz. It does not matter if the instrument is really made of brass, as long as it works that way.
It is not important what the instrument is made of. Some brass instruments are really made of wood, but are still called brass instruments, like the serpent. Other instruments are made of brass but do not work like this, like the saxophone. They are not called brass instruments although they are made of brass.
A brass band is a group of brass instruments and drums that play music together. They are often used to play for parades and processions because the players can march and play at the same time. Brass bands were very popular in England. Many factories and coal mines had their own bands. The workers would play in the bands after work. One famous band is the Grimethorpe Colliery Band.