A "boom arm" attaches to the top of the stand so the microphone can move in the horizontal plane. A guitar player, for example, might use this to place the microphone directly in front of his mouth without having the upright portion of the stand in the way of the guitar. It also lets musicians have the microphone closer to the sound source when floor space is at a premium. This can be particularly useful when placing microphones on a drum stand when the microphone stands must compete for space with things like cymbal stands. Boom arms are offered both in fixed length and adjustable (telescoping) lengths.
