Event-driven systems are architectures that respond to events or changes in state rather than following a predetermined sequence of operations. In these systems, an event can be anything from a user action, like clicking a button, to a system-generated signal, such as a timer expiring. This approach allows for more flexible and responsive applications, as components can react to events as they occur. In an event-driven system, components communicate through events, often using a message broker or event bus. This decouples the components, allowing them to operate independently and scale more easily. Common examples of event-driven systems include microservices, real-time data processing, and user interface applications.