What river and all of its tributaries make up is called?

A river and all of its tributaries together form a river system or a river basin. The main river is often referred to as the "parent" river, while the smaller streams and rivers that feed into it are called tributaries. This interconnected network of waterways is crucial for drainage, ecosystem health, and water resource management. An example of such a system is the Mississippi River and its numerous tributaries, including the Missouri and Ohio Rivers.