The term used to describe the disease condition caused by the improper functioning of the posterior lobe of the pituitary gland is known as "Diabetes Insipidus". This gland produces a hormone called antidiuretic hormone (ADH) or vasopressin, which controls the amount of water excreted in the urine and regulates the water balance in the body. When there is a deficiency or malfunction of ADH, it results in excessive urination and thirst, leading to dehydration, electrolyte imbalances, and other complications if not treated appropriately.