The euphonium is a brass instrument. It is very similar to the baritone horn, but it is different because the tubes are wider and it is bigger. The euphonium makes low sounds, similar to the trombone. The euphonium has 3 or 4 valves and 1-3 spit valves. "Spit" valves do not really mean there is spit in the instrument, it means that there is condensation in the instrument.
The euphonium is seen in different sorts of bands in Europe and America. The musicians make the sound by blowing into the instrument and "buzzing" with their lips.
The word euphonium means: "producing nice sounds"