Cushing's syndrome
Strictly, Cushing's syndrome refers to excess cortisol of any etiology (as syndrome means a group of symptoms). One of the causes of Cushing's syndrome is a cortisol-secreting adenoma in the cortex of the adrenal gland (primary hypercortisolism/hypercorticism). The adenoma causes cortisol levels in the blood to be very high, and negative feedback on the pituitary from the high cortisol levels causes ACTH levels to be very low.