The word you use to describe a group of specialized organs that work together to perform a major function is organ system.

For example:

* Digestive system - composed of organs like the mouth, esophagus, stomach, intestines, etc., that work together to break down food.

* Circulatory system - composed of organs like the heart, blood vessels, and blood, that work together to transport blood throughout the body.

* Nervous system - composed of organs like the brain, spinal cord, and nerves, that work together to receive and transmit information.

Let me know if you have any other questions!