What HTTP response codes do you know? What do 401, 403, 500 mean?

Here are the main HTTP response codes and their meanings:

• 200 OK — the request was successful.
• 201 Created — the resource was successfully created.
• 400 Bad Request — invalid request, client error.
• 401 Unauthorized — not authorized, authentication required.
• 403 Forbidden — access is denied, even if authenticated.
• 404 Not Found — resource not found.
• 500 Internal Server Error — internal server error.
• 502 Bad Gateway — the server received an invalid response from another server.

What they specifically mean:

• 401 Unauthorized — the client did not provide correct credentials or is not authorized. Usually, the server requires login/password.
• 403 Forbidden — the client is authenticated but does not have permission to access the resource.
• 500 Internal Server Error — an error on the server side that is not related to the client's request, such as a bug in the code or database.