The Secure Sockets Layer (SSL) is a mechanism for wrapping network communication in a security layer that can be used to encrypt communication between the client and the server. It also provides an integrity mechanism to ensure that the communication is not altered between the client and the server. The encryption is based on cryptography using certificate.
SSL was originally a proprietary protocol developed by Netscape Communications. It has since been standardized, but the name has been changed to Transport Security Layer. Nevertheless, SSL is still a commonly-used term to refer to this capability, and it is the term used throughout the directory server in order to avoid confusion with the StartTLS extended operation.