Hypothyroidism is a condition where the thyroid gland does not produce enough hormones to regulate the body's metabolism. This condition affects millions of people worldwide and can cause fatigue, weight gain, and depression. There are several synonyms for hypothyroidism, including underactive thyroid, thyroid insufficiency, and myxedema. Other terms that are sometimes used include thyroid hormone deficiency, thyroid dysfunction, and thyroidal hypofunction. It's essential to recognize the signs and symptoms of hypothyroidism and to seek medical attention if you suspect you have this condition. Early diagnosis and treatment can help prevent further complications and improve your quality of life.