A goiter is a swelling or enlargement in the neck, caused by an abnormal growth of the thyroid gland. It can be due to various reasons such as iodine deficiency, autoimmune disorders, or congenital conditions. The term "goiter" refers specifically to the visible mass formed by the swollen thyroid gland, and may cause symptoms like difficulty in swallowing or breathing, hoarseness, or a feeling of tightness in the throat.