A Baritone horn (also known as a baritone) is a musical instrument like a tuba but smaller and higher pitched. it is a brass instrument, and it usually is played primarily in bass clef. It has effectively the same sound as a trombone. The baritone is very similar to a euphonium, but baritones are typically smaller.
Marching baritones are used by marching bands. These can feel very heavy because the person playing it holds it up with only their arms. Marching baritones look like a big trumpet but the tubing is much larger.
