Original: Graves' disease is an autoimmune disease where the thyroid is overactive, producing an excessive amount of thyroid hormones (a serious metabolic imbalance known as hyperthyroidism and thyrotoxicosis).
Simplified: Graves' disease 'is an autoimmune disease of the thyroid. In people affected by the disease, the thyroid produces a bigger quantity of hormones than normal, which is commonly known as hyperthyroidism.