The word trombone derives from Italian tromba - meaning trumpet - and one - a suffix for "large." Thus, quite literally, a trombone is a "big trumpet." In symphonic literature, the trombone is referred to by its name in other languages, e.g. posaune, sackbut or sacbut, basun, tromba spezzata.
The trombone consists of a cylindrical tube bent into an elongated "S" shape (it is interesting to note that in French, trombone also means "paper clip"). Most trombones are slide trombones;. The section immediately following the mouthpiece is a short straight length of tube called the lead pipe. Below that is the slide, which allows the player to extend the length of the instrument, lowering the pitch. Some trombones have valves instead: see valve trombone, below.
Until around the 18th century, the trombone was called the sackbut (literally, "pull - push" in French) in English. This was not a distinct instrument from the trombone, but rather a different name used for an earlier form (other countries used the same name throughout the instrument's history). The sackbut was slightly smaller than modern trombones, and had a bell that was more conical and less flared. Today, sackbut is generally used to refer to the earlier form of the instrument, commonly used in early music ensembles.
Trombones come in five sizes: soprano, alto, tenor, and bass, and contrabass.
The standard tenor trombone has a fundamental note of B flat (yet is usually treated as nontransposing, see below). Since trombones have no valves or keys to change the pitch by a definite amount, trombonists memorize seven slide positions. The slide is said to be in "first position" when it is retracted all the way, and in "seventh position" when it is almost completely extended. Extending the slide from one position to the next lowers the pitch by one semitone; thus, for each note in the harmonic series a downwards interval of up to a tritone may be added to the 1st position note, taking the lowest note of the standard instrument to E natural below the bass clef. Trombones often come with an extra piece of tubing attached, allowing the player to lower the pitch by a fourth by pulling a trigger, making faster passages and legato playing easier, and extending downwards the range of the basic tenor trombone. Playing with this trigger ( called colloquially in Britain and the Commonwealth 'a plug) down modifies the set of positions; the distance between each is longer due to the lowered pitch. In fact, there are only six real positions available to the player, since the slide is too short for what is now really a trombone in F.
The modern bass trombone is also built in Bb and played in C. It is basically the same length as the tenor trombone but has a larger bore size, and has two valves, generally in F and D (although sometimes Eb), which change the key of the instrument, making it easier to play lower notes. This also allows the player to bridge the entire gap between the first harmonic and the fundamental. The notes on the bass trombone are played in the same position on the slide as the tenor trombone (until you start using the valves). There is usually one bass trombone player in a standard symphony orchestra, and they are also often seen in swing bands, wind ensembles, and a variety of brass groups. Wagner's Ring Cycle also calls for a contrabass trombone, pitched in BBb, an octave lower than the tenor trombone. Earlier versions of the bass trombone were of smaller bore than modern bass trombones described above. These were pitched in 'G', had a longer slide and a handle attached to the slide to allow for full extension to seventh position.
The alto trombone is pitched in E-flat or F, and is smaller than the tenor trombone. Because of its shorter length, the slide positions are different than on the tenor and bass trombones. The tone of the alto is more brilliant than that of the tenor or bass trombone. The alto trombone is primarily used in symphonic settings, although it has enjoyed a history as a solo instrument. Modern composers have rediscovered the instrument and the alto trombone has begun making more appearances in modern compositions. Modern professional tenor trombonists in the classical music realm are increasingly expected to also have fluency on alto trombone.
The soprano trombone is an even shorter instrument, and offers a brighter, more trumpet-like sound than any other trombone. Essentially a "slide-trumpet" (its mouthpiece is generally a trumpet mouthpiece), scores for the soprano trombone are found in trombone choir and other brass ensembles, though few classical pieces call for the instrument. Indeed, the history of the soprano trombone is questionable, and it may be that the instrument is not a classical instrument at all, but a more modern derivation of the trombone.
Valve trombones have the same tonal range as a tenor trombone but a somewhat different attack, as they are shaped more like very large trumpets. Some musicians consider them difficult to play in tune, although a small minority (often former trumpeters whose embouchures are more suitable to lower-ranged instruments but prefer not to learn slide technique) prefer them to the more common slide trombone. Other instruments with similar range and tone quality are the baritone horn and euphonium. Wagner also wrote a part for a bass trumpet in his Ring Cycle; this part is normally played by a trombonist. A handful of other works in the classical repertoire also use this instrument.
A variety of mutess can be used with the trombone to alter its timbre, including the wah-wah mute. In addition to mutes which are fitted inside the bell of the horn, other effects are used (especially in jazz playing) with objects held in the hand in front of the bell or moved in and out of the bell. These include a wah waha effect with a metal cup which looks like a bowler hat, and the plunger, which looks like, and often is, the rubber suction cup from a toilet plunger).
The trombone (unlike most brass instruments) is not normally a transposing instrument and reads the bass clef (especially bass trombones), although it is not uncommon for trombone music to be written in tenor clef, or sometimes even alto clef. In brass band music, however, the trombone is treated as a transposing instrument in Bb and reads the treble clef. By happy coincidence, this puts the notes in exactly the same stave position as they would be if the music were written in a (non-transposing) tenor clef, though the key signature must be adjusted.
As with all brass instruments, progressive tightening of the lips (and increased air pressure) allows the player to jump to a different partial, up the harmonic series. In the lower range, significant movement of the slide is required, but for higher notes the player need only use four or fewer positions of the slide, since the partials are closer together, allowing higher notes to be played in alternate positions; for example, F natural (at the bottom of the treble clef) may be played in both first, fourth and sixth positions.