Session Initiation Protocol (SIP) response codes are three-digit numbers used to convey critical status information during phone calls or communication sessions over SIP. These codes, grouped into categories like informational responses, success responses, redirection responses, client error responses, server error responses, and global failure responses, serve as a common language that allows various components of a communication system to communicate effectively and handle calls appropriately. Understanding these codes is crucial for troubleshooting and identifying the status of a communication session, ensuring smoother call operations, and providing better customer experiences.