CORS
Answer out loud or in your head first, then compare.
Answer
CORS is a mechanism where the server uses headers to say whether the browser may share a response with a script from another origin. An origin is the scheme, host and port.
For some requests the browser first sends an OPTIONS preflight, asking which method and headers are allowed.
Example: a frontend on a different port from the API needs the right configuration on the API side.
Pitfall: CORS is not authentication, a firewall or protection against every request. Some requests can reach the server even though JS can't read the response. With credentials you can't use Access-Control-Allow-Origin: *. no-cors doesn't let you read the response freely.
How did it go? Be honest — “Not yet” puts the question on your review list.