The HTTP Status Codes are essential with the communication of the requesting device.
Firstly, the server sends the codes to the requesting device. To clarify, these codes let the requesting device know how to handle the connection. The hosting server is basically telling the requesting device how to handle the request and what to do next.
For example, listed below are the most common common codes. For a complete list of HTTP Status Codes, please visit IANA. To clarify, they are responsible for maintaining the code registry.
Relating to HTTP Status
200 OK - Successful connection.
301 Moved Permanently - The link you are attempting to connect has been redirected. Future requests should connect to the new link.
302 Found - The link you are attempting to connect has been temporarily redirected. Future requests should continue to use the same link.
400 Bad Request - The server to which you are trying to connect could not understand the request. Modify the link before any future connections.
401 Unauthorized - The requested link requires user authentication.
403 Forbidden - The server is refusing the request.
404 Not Found - The server was unable to match the request. This could be temporary or permanent.
500 Internal Server Error - The server prevents from completing the request.
503 Service Unavailable - The server is unable to complete the request at this time. This is usually a temporary condition.
FTP Server Return Codes - FTP server return codes are sent from the FTP server to the requesting device to let the requesting device know where the connection stands.