The TLS protocol is the successor toSSL. It was introduced in 1999 as an improved version of SSL 3.0 and was called SSL 3.1 at first. The current version is TLS 1.3 (as of 2018).
The jump from SSL 3.0 to TLS 1.0 was initially just a small one. “The differences between this protocol and SSL 3.0 are not dramatic, but they are significant enough that TLS 1.0 and SSL 3.0 do not interoperate” (RFC 2246). Compared to SSL 3.0, TLS 1.0 improved cryptographic security and application interoperability. The currently used version TLS 1.2 provides increased security against hacker attacks and allows applications much more flexibility with regard to the encryption used (cipher suites).
The current version of TLS is more secure, flexible, and efficient than its predecessor SSL. Since the acronym SSL is still much more widely known than TLS, many providers of client software, routers, and so forth use the term SSL or alternatively the combined term SSL/TLS. However, this is usually referring to the current version of TLS (i.e. TLS 1.3).