HTTP status codes are three-digit numerical codes returned by a web server to a client (typically a web browser) in response to a request. They indicate the outcome of the request and provide information about the status of the connection.
Five classes of HTTP status codes:
1xx (Informational): The request was received, and the server continues to process it.
2xx (Successful): The request was received, understood, and accepted. This class’s most common status codes are 200 OK and 201 Created.
3xx (Redirection): The request must be redirected to a different location to be fulfilled. The most common status code in this class is 301 Moved Permanently.
4xx (Client Error): The request contains bad syntax or cannot be fulfilled by the server. This class’s most common status codes are 400 Bad Request and 404 Not Found.
5xx (Server Error): The server failed to fulfill a valid request. The most common status code in this class is 500 Internal Server Error.
It’s important to note that HTTP status codes are not only used for web pages. It is also used for API calls, data transfer via HTTP, etc.
Also, See: Secure Shell (SSH)