SASL (Simple Authentication and Security Layer) is a framework for providing authentication and data security services in Internet protocols. It is a protocol-independent method that allows for the addition of different authentication mechanisms to connection-based protocols without modifying the underlying protocol itself.

GSSAPI (Generic Security Service Application Program Interface) is an API that provides security services to applications. It allows applications to communicate securely over a network by providing a generic interface for various security mechanisms. GSSAPI supports different security mechanisms, including Kerberos, NTLM, and others, which can be used for authentication, integrity, and confidentiality protection.

SASL/GSSAPI is a combination of the two, where GSSAPI is used as an authentication mechanism within the SASL framework. This combination provides a standardized, extensible method for secure authentication in various Internet protocols, such as LDAP, IMAP, and SMTP. By using SASL/GSSAPI, applications can leverage the security services provided by GSSAPI while maintaining protocol independence and flexibility offered by SASL. This approach simplifies the process of adding and managing authentication mechanisms in different protocols and applications.