Definition for rivers and streams

A river is a natural flow of running water that follows as well-defined, permanent path usually within a valley.

A stream is natural flow of water that follows a more temporary path that is usually not in a valley

Answer;

river and streams are types of open channels i. e. conducts of water with a free surface in contrast to canals, ditches and adequate. river and streams are the products of natural geological processes and as a consequences are quite irregular.