[Asynchronous vs synchronous (non-blocking, concurrent vs blocking, sequential)] Events are messages used with a runtime scheduler called an event loop that dispatches messages from a message queue (message bus) to event handlers.

Event-based or event-driven models are typically used to implement concurrency while avoiding the expensive blocking of system threads (expensive due to the overhead of stack-based memory allocation), expensive system thread context switches and the complexity of managing locks with shared memory (the conventional communication model for system threads). A low-level counterpart of event handlers are hardware interrupt handlers.