Secure Sockets Layer (SSL) is a protocol that was created by Netscape in the 1990s. The main purpose of SSL was to provide security for Internet connections by ensuring confidentiality, authentication, and integrity for the data transported by it. To standardize SSL, Internet Engineering Task Force (IETF) in 1999 proposed a standard version which was termed as Transport Layer Security (TLS) in RFC 2246. It is worth mentioning here that both SSL and TLS act between the transport layer and the session layer.
The above diagram depicts where SSL fits in OSI model.