HTTP status codes are three-digit numbers returned by a server to indicate the outcome of a client’s request. They provide information about the status of the request and the server's response.

200 series (Success)

• 200 OK: The request was successful, and the server returned the requested resource.
• 204 No Content: The request was successful, but there is no content to send in the response

300 series (Redirection)

• 301 Moved Permanently: The requested resource has been moved to a new URL permanently. The client should use the new URL provided in the response.
• 304 Not Modified: The resource has not been modified since the last request. The client can use the cached version.

400 series (Client Error)

• 400 Bad Request: The server could not understand the request due to invalid syntax.
• 401 Unauthorized: The request requires user authentication. The client must provide credentials.
• 403 Forbidden: The server understood the request but refuses to authorize it.
• 404 Not Found: The requested resource could not be found on the server.

500 series (Server Error)

• 500 Internal Server Error: The server encountered an unexpected condition that prevented it from fulfilling the request.
• 502 Bad Gateway: The server received an invalid response from an upstream server while acting as a gateway or proxy.