What exactly is adrenal insufficiency?

Adrenal cortex loss: Hi. Adrenal deficiency refers to Addison's disease, primary adrenal cortical failure, where the body is deficient in two vital adrenal cortical steroid hormones, cortisol and aldosterone. Central/pituitary adrenal insufficiency is deficient only in cortisol (not aldosterone). Cortisol is a vital "stress" hormone, and is necessary for life in the long run and the acute physiologic stress setting.