The larynx was an organ in the neck of some creatures that moderated breathing and sound production.
The Fourth Doctor stated that Time Lord larynxes were able to "stand up to anything", explaining why his voice was not affected by inhaling helium. (TV: The Robots of Death)
Cepholans had three larynxes. (PROSE: Tomb of Valdemar)
The Tythonian communicator enabled Tythonians to communicate by controlling the larynx of whoever touched it. (TV: The Creature from the Pit)
Davros' larynx was damaged in an attack, and was replaced with a voice box. (AUDIO: Davros)