Thyroid diseases refer to a range of conditions that affect the thyroid gland, a butterfly-shaped gland located in the neck. This gland produces hormones that regulate metabolism, energy levels, and overall body function. Common thyroid diseases include hypothyroidism, where the gland does not produce enough hormones, and hyperthyroidism, where it produces too much. Other thyroid conditions include goiter, an enlargement of the gland, and thyroid nodules, which are lumps that can form in the gland. Hashimoto's thyroiditis is an autoimmune disorder that can lead to hypothyroidism, while Graves' disease is an autoimmune condition that causes hyperthyroidism.