Dyspnea was a medical term describing a sensation of difficulty in breathing.
Dyspnea was generally considered a symptom of disease. In some species, such as Tellarites, it was considered a sign. (The difference between a symptom and a sign was that a symptom was something that might be noticed by the patient or an untrained layman, whereas a sign was something that only a trained medical professional would spot.)
Doctor Julian Bashir downloaded data about dyspnea, coughing, and other pulmonary disorders onto a PADD shortly before he left to attend a medical conference on Casperia Prime in 2374. (DS9: "Inquisition")