CORS

Cross-Origin Resource Sharing

Browser mechanism letting servers permit cross-origin requests.

When you'd see it: Front-end development, especially when a web app calls an API on a different domain. The "CORS error" is one of the most common browser console messages.

Why it matters: CORS is the browser rule controlling which other domains may call your API from a user's browser. It is a security boundary, not a bug, even though it usually shows up as a blocked request.

Common mistakes: Disabling CORS entirely to make the error disappear. That removes a real protection. The fix is allowing the specific origins you trust, not allowing all of them.