What is CORS? If two backend servers communicate without a browser, will CORS occur?

CORS (Cross-Origin Resource Sharing) is a browser security mechanism that restricts requests from one domain to resources on another domain unless the server explicitly permits such access through special headers.

If two backend servers communicate directly with each other (for example, via HTTP requests without involving a browser), CORS does not apply, as this restriction is implemented specifically on the browser side to protect users. Servers can freely exchange data without CORS restrictions.