Sinusitis refers to inflammation of the sinuses, which are hollow cavities located around the nasal passages. It can be caused by infections, allergies, or structural issues that block the sinuses. Symptoms include facial pain, nasal congestion, headaches, and loss of smell. Treatment may involve self-care, medications, sinus irrigation, or surgery to improve drainage and relieve symptoms. Maintaining good nasal hygiene and managing allergies can help prevent sinusitis.