Mucus is a slimy substance produced by the body to help protect and lubricate the respiratory system. It is made up of water, proteins, carbohydrates, and lipids. PHLEGM is a type of mucus that is produced in the lungs and is usually expelled through coughing. SPUTUM is another type of mucus that is produced in the airways and is usually expelled through coughing or spitting. Both PHLEGM and SPUTUM are important for keeping the respiratory system healthy.