Parathyroid gland: A gland that regulates calcium, located behind the thyroid gland in the neck. The parathyroid gland secretes a hormone called parathormone (or parathyrin) that is critical to calcium and phosphorus metabolism. Although the number of parathyroid glands can vary, most people have four, one above the other on each side. They are plastered against the back of the thyroid and therefore at risk for being accidentally removed during thyroidectomy.
