The low brass section of an orchestra contains many instruments - all but one are not widely known. Hence, the low brass section is one of the least acclaimed sections of the orchestra.
The trombone, or T-bone, is truly the most unique of the brass instruments. It does not use valves like the others, but instead uses a single slide that is moved to lengthen or shorten the horn and make the pitch go higher/lower. Trombonists are often very protective of their instrument, for it is rather easy to damage. Variations of the instrument often feature one or more keys. These can be used in place of certain slide positions, especially the ones that reach out really far and run the risk of breaking one's elbow.
The baritone, or B-Tone, is very similar to a little tuba. Many people often mistake it for a little tuba. Others just call it 'the little tuba'. However, there are numerous differences between the baritone and tuba. For instance, the baritone is much, much smaller than the tuba. It also has a much higher pitch and may even be in a different clef. This allows the player, if very skilled, to bring up the pitch into the trumpet range. Variations of the baritone include the euphonium, which is similar in size and range but has one or two more valves than the baritone. Another variation is the marching baritone or 'Ghetto Trumpet'. It is much easier to carry and is similar to a large trumpet.
The tuba is probably the most well-known low brass instrument. It is large, low pitched, and requires a huge amount of air to play. A variation of this instrument is the sousaphone. It is also large, but wraps around its player so that it can be carried much easier. It was invented by John Phillip Sousa.