What term is used to describe a complete living entity made of various organ systems?

The term that describes a complete living entity made of various organ systems is "organism." An organism is an individual living thing, distinguished by the ability to carry out all life processes such as growth, reproduction, response to stimuli, and metabolism. It encompasses numerous organ systems that work collaboratively to maintain homeostasis and ensure survival.

For example, in humans, different organ systems like the circulatory system, respiratory system, and digestive system come together to support the organism's overall functioning. Each organ system consists of various organs, which in turn are made up of tissues, and those tissues are composed of cells. Thus, an organism represents the highest level of biological organization where multiple systems are interdependent and work as a whole unit.