Homeostasis: A property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly. Homeostasis is a healthy state that is maintained by the constant adjustment of biochemical and physiological pathways. An example of homeostasis is the maintenance of a constant blood pressure in the human body through a series of fine adjustments in the normal range of function of the hormonal, neuromuscular, and cardiovascular systems. These adjustments allow the maintenance of blood pressure needed for body function despite environmental changes and changes in a person's activity level and position. Other homeostatic mechanisms, for example, permit the maintenance of body temperature within a narrow range.