Phlegm is a thick, viscous fluid produced by the mucous membranes in the respiratory system. It plays an important role in protecting the respiratory tract by trapping dust, microbes, and other particulate matter, making it easier for the body to expel them. Phlegm is often associated with illness, particularly colds and respiratory infections, and can vary in color and consistency.
The word "phlegm" originates from the Latin word "phlegma," which in turn comes from the Greek word "phlegma," meaning "inflammation" or "heat." This reflects the historical association of phlegm with bodily humors and illnesses.