SSL refers to Secure Sockets Layer, a security protocol that has been replaced by Transport Layer Security (TLS). TLS is still commonly referred to as SSL.
The SSL protocol provides privacy and integrity of data between two applications that communicate over the Internet. This occurs through the authentication of the parts involved and the number of data transmitted between them. This protocol helps prevent intermediaries between the two ends of the communication have unauthorized access or falsifying the data transmitted.
The site server being accessed sends a public key to the browser, used by this call to send a secret, randomly created. Thus, it is established to exchange encrypted data between two computers.
It is based on the TCP protocol suite TCP / IP and utilizes the concept introduced by Diffie-Hellman in the 70s (public key cryptography) and Phil Zimmermann (PGP creator of the concept).