HTTP Status Codes are standardized responses from a web server to a client's request, indicating the outcome of that request. These codes are grouped into five categories: informational (100-199), success (200-299), redirection (300-399), client error (400-499), and server error (500-599). Each code provides specific information about the request's status, helping users and developers understand what happened. For example, a 200 OK status means the request was successful, while a 404 Not Found indicates that the requested resource could not be found on the server. Understanding these codes is essential for troubleshooting and improving web applications.