A slide control. It uses a single slide valve rather than individual smaller valves to change the pitch of the instrument.
A trombone has a slide, which other brass instruments lack.
The trombone isn't a stringed instrument. so it has a lot of things that stringed instruments don't have. Like a mouthpiece.
A trombone has a slide. The slide allows it to do the infamous glissandos.
It has a slide, rather than buttons.
It has a slide, rather than buttons.
The trombone mouthpiece is exactly the same as an euphonium one. You may also (with difficulty) manage to play a Bass Trombone or Tuba with a tenor trombone mute
A slide
All the other brass instruments because they have valves.
Trumpet, trombone, and tuba are all brass instruments. The other is a percussion instrument.
The trombone is the only instrument in the brass section with no keys or valves. It only has a slide.
The trombone has a slide that can be moved to change the pitch of notes rather than valves or keys that lengthen the tubing to change the pitch of notes like other brass instruments. And there are a lot more than 3 other brass instruments.
The most common low brass instruments are: 1. Trombone (bass trombone is lower than tenor trombone) 2. Euphonium & baritone horn 3. Tuba