The pituitary is called 'master gland' because

The pituitary gland is called the 'master gland' because it controls the functions of many other glands in the body. It does this by producing and secreting hormones that stimulate or inhibit the production of hormones from other glands. So, it acts as a central regulator of the endocrine system, which is responsible for maintaining the body's internal balance and regulating various physiological processes. Additionally, the pituitary gland is located in the brain and is connected to the hypothalamus, which is a key region that controls many essential bodily functions such as hunger, thirst, and temperature regulation.