Events are a concurrency scheme that are an alternative to thread-based concurrency. They’re popular primarily in JavaScript/TypeScript, where they’ve seen wide adoption in browsers and runtimes (like Node.js).
Events use an event loop that iterates through the list of events. When something of note happens, it triggers a call-back function that runs.
Language-specific
In C
C provides event-based concurrency via the select() and poll() syscalls.