A System is a regularly interacting or interdependent group of items forming a unified whole (Merriam-Webster). Example: digestive system, automotive system, plumbing system, etc.
Think about your classroom as a system. Define the system: the parts, the function of each part, and the purpose. Write a paragraph that explains how the parts affect one another. For example, you might think about how your students interact, how you affect your students, and how an interruption affects the classroom system.