The thyroid gland is a butterfly-shaped gland located below and to the sides of the trachea and esophagus and above to the larynx, that is, in the neck. The thyroid gland creates hormones that regulate metabolism.
When the thyroid malfunctions, you'll end up with either hyperthyroidism (too much hormone) or hypothyroidism (too little). Women in particular may be susceptible to Hashimoto's thyroiditis, an auto-immune disease that causes your immune system to attack your thyroid (results in hypothyroidism).