What is "mellophone"

n. A brass instrument frequently used in place of the French horn in marching bands and similar performance groups

The mellophone is a three-valved brass instrument pitched in the key of F or E♭. It has a conical bore, like that of the euphonium and flugelhorn. The mellophone is used as the middle-voiced brass instrument in marching bands and drum and bugle corps in place of French horns, and can also be used to play French horn parts in concert bands and orchestras.

These instruments are used instead of French horns for marching because their bells face forward instead of to the back (or to the side), as dissipation of the sound becomes a concern in the open-air environment of marching. Tuning is done solely by adjusting the piping, instead of adjusting both piping and hand position as on the French horn. Fingerings for the mellophone are the same as fingerings for the trumpet, alto (tenor) horn, and most valved brass instruments. Owing to its use primarily outside of concert music, there is little solo literature for the mellophone, other than that used within drum and bugle corps.