Is sputum another word for Phlegm?

Sputum and phlegm are often used interchangeably, but there is a slight difference between the two. Sputum refers to the thick, viscous fluid that is expelled from the respiratory tract during coughing, while phlegm is a more general term that can refer to any type of mucus or other fluid that is produced in the respiratory tract. Sputum is typically produced in the lungs and bronchi, while phlegm can also be produced in the nose, throat, or sinuses. Additionally, sputum is typically thicker and more opaque than phlegm.