The glottis was the space between an individual's vocal cords. It was instrumental in producing hiccups, which Data described as "a spasmodic inhalation with closure of the glottis, accompanied by a peculiar sound. ". (TNG: "We'll Always Have Paris")
"The Klingon Glottis: Friend or Foe?" was one of the proposed themes for "Hints for Healthful Living", The Doctor's segment in Neelix's program A Briefing with Neelix. (VOY: "Investigations")