The term "Eustachian" primarily refers to the Eustachian tube, a narrow passage that connects the middle ear to the back of the throat. This tube helps equalize air pressure on both sides of the eardrum, which is essential for proper hearing. It also allows drainage of fluids from the middle ear, helping to prevent infections. The Eustachian tube opens during activities like swallowing or yawning, which can help relieve pressure changes, such as those experienced during air travel. Dysfunction of the tube can lead to issues like ear pain, muffled hearing, or otitis media, an infection of the middle ear.