Status codes are standardized numerical responses used by web servers to communicate the outcome of a client's request. These codes are part of the HTTP protocol and help users and developers understand whether a request was successful, encountered an error, or requires further action. Common status codes include 200 OK for successful requests, 404 Not Found for missing resources, and 500 Internal Server Error for server issues. Each status code consists of three digits, with the first digit indicating the response category. For example, codes starting with 2 signify success, while those beginning with 4 indicate client errors, and codes starting with 5 represent server errors. Understanding these codes is essential for troubleshooting and improving web applications.