Conjunctivitis is an inflammation or infection of the conjunctiva, which is a thin layer of tissue that lines the inside of the eyelid and covers the white part of the eye. It can be caused by various factors such as bacteria, viruses, allergies, or chemical irritants. Symptoms may include redness, swelling, itching, tearing, and a discharge from the eyes. Conjunctivitis is commonly known as "pink eye" due to its characteristic appearance of the affected eye(s).