Secure Sockets Layer (SSL) is a cryptographic protocol that protects communications over insecure networks, such as the Internet. SSL establishes a session between a client and a server through a handshake to authenticate the identities of the communicating parties and negotiate keys and cipher suites. This prevents the interception of communication between the client and server and secures data transmission on the network. SSL certificates are used to authenticate and establish a secure connection between a client and a server.