A nasal cannula is a medical device used to deliver supplemental oxygen to patients who need help breathing. It consists of a thin tube that splits into two prongs, which are placed in the nostrils. The other end of the tube connects to an oxygen tank or oxygen concentrator, allowing for a steady flow of oxygen. Nasal cannulas are commonly used in hospitals, clinics, and at home for patients with respiratory conditions like COPD or asthma. They are preferred for their comfort and ease of use, allowing patients to talk and eat while receiving oxygen therapy.