Otitis media with effusion, also known as serous otitis media or glue ear, is a condition where the middle ear fills with fluid without signs of active infection. It often occurs after acute ear infections and may be caused by Eustachian tube dysfunction or risk factors like cleft palate or common colds. Diagnosis involves tympanometry to measure eardrum mobility and audiometry to identify conductive hearing loss, while treatment focuses on fluid resolution through watchful waiting, medication, or ear tube insertion for persistent cases.