Chaos Monkey is a tool developed by Netflix to improve the reliability of cloud-based applications. It randomly terminates instances of services in a production environment to test how well the system can handle unexpected failures. This practice helps teams identify weaknesses and improve their response to real outages. By simulating failures, Chaos Monkey encourages developers to build resilient systems that can recover quickly. It is part of a broader suite of tools known as Simian Army, which aims to enhance the robustness of cloud infrastructure through various forms of chaos engineering.