A status code is a three-digit number returned by a server in response to a client's request, typically in the context of web development. These codes indicate the outcome of the request, helping users and developers understand whether the request was successful, encountered an error, or requires further action. Common status codes include 200 for success, 404 for not found, and 500 for server errors. Status codes are part of the HTTP protocol, which governs how messages are formatted and transmitted on the web. They are essential for diagnosing issues, optimizing user experience, and ensuring proper communication between clients, such as web browsers, and servers.