Located in the middle of the neck, the butterfly-shaped thyroid gland is responsible for producing thyroid hormones. These hormones are imperative in maintaining the body's metabolism.
Hypothyroidism refers to underactivity of the thyroid gland. When the thyroid gland is underactive, it produces insufficient thyroid hormone which could cause a "slowing down" of various bodily functions.
Another way the thyroid gland could malfunction is by producing excessive thyroid hormone. This condition is known as hyperthyroidism, learn more about hyperthyroidism here.