Cushing's Disease is a rare endocrine disorder caused by a benign tumor of the pituitary gland, which leads to overproduction of the adrenocorticotropic hormone (ACTH). This, in turn, stimulates the adrenal glands to release excessive amounts of cortisol, known as the "stress hormone." 

Unlike Cushing's Syndrome, which includes any cause of excess cortisol, Cushing's Disease specifically refers to pituitary-dependent causes and accounts for a significant percentage of endogenous Cushing's Syndrome cases.

The pituitary gland, often dubbed the "master endocrine gland," orchestrates the hormone balance in the body. A malfunction in this gland can have widespread effects due to the excess cortisol circulating in the body.