What does the diagnosis "hyperthyroidism secondary to graves' disease" mean in layman's terms?

Graves disease: It means you have graves disease causing your thyroid to produce too much hormones. It doesn't go away on its own and will need to be treated.

See below.: It means graves' disease is the cause of your hyperthyroidism. Hyperthyroidism just means you have too much thyroid hormone. There can be several reasons for that; graves' is one of the common ones.