Secure Socket Layer (SSL): A cryptographic protocol designed to provide secure communications over a computer network. SSL uses a combination of public key and symmetric key encryption to secure a connection between two machines, typically a web server and a client, over the internet. It was widely used for securing data transfer, ensuring the privacy and integrity of information, and verifying the identity of parties involved in the communication through the use of digital certificates. SSL has been superseded by Transport Layer Security (TLS), an updated and more secure version of the protocol, and while the term SSL is still commonly used, most underlying systems actually use TLS.