Trombones are a family of brass instruments characterized by their adjustable slides. Trombones actually come in a consort, including the contrabass, G bass, Bb bass, symphonic (large bore) tenor, jazz (small bore) tenor, Eb alto, F alto, soprano, and sopranino trombones. In general, the lower-pitched the instrument, the easier pitch is to control given the larger slide movement relative to the same pitch adjustment on the larger instruments.
Trombones are usually written in concert pitch, with a couple of exceptions.
Contrabass, G bass, Bb bass, and the tenor trombones are all written in bass clef, untransposed. Tenor trombones can also be written in untransposed tenor clef, and occasionally (in British brass bands) in treble clef transposed up a major ninth.
Alto trombones are written in untransposed alto clef.
Soprano trombones are usually written in treble clef, transposed up a whole step, the same as Bb trumpets.
Like most brass instruments, trombones sound on an approximated overtone series, and their ability to gliss encompasses tritones descending downward from each partial. For example, tenor trombones, pitched in Bb have partials of Bb-Bb-F-Bb-D-F-Ab-Bb . . . as per a 1:2:3:4:5:6:7:8 . . . overtone series, and the glisses can descend a tritone down from each of those partials. This system gives trombones unparalled pitch sensitivity compared to other brass instruments, and in expert hands, trombones are extremely versatile, capable of being extremely lyrical, blending, or raucus as the orchestration requires.
Because trombone slides are 'fretless' and incapable of having frets added, trombones are probably best-suited for intonation systems closely related to just intonation, where the performer's ear can more easily identify points of consonance, rather than intonation systems which avoid consonant points where it can be extremely difficult to find a 'point of instability' by ear.