A Service Principal Name (SPN) is a unique identifier for a service instance in a network, primarily used with Kerberos authentication in Windows environments. SPNs allow clients to uniquely identify and authenticate services such as web servers, databases, or other network applications. When a client requests access to a service, the SPN helps Kerberos locate the correct account associated with that service, ensuring secure authentication. Proper configuration and management of SPNs are critical to prevent authentication failures and security vulnerabilities, such as service spoofing or unauthorized access. Administrators must ensure that each SPN is unique and correctly mapped to its service account.