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 connects to an oxygen source, allowing for a steady flow of oxygen to be inhaled. Nasal cannulas are commonly used in hospitals and at home for patients with respiratory conditions like chronic obstructive pulmonary disease (COPD) or asthma. They are preferred for their comfort and ease of use, allowing patients to talk and eat while receiving oxygen therapy.