Definition
Secure Sockets Layer was developed by Netscape in the mid-1990s to encrypt traffic between web browsers and servers. SSL 2.0 (1995) and SSL 3.0 (1996) had serious vulnerabilities and have been deprecated for many years; SSL 3.0 was specifically broken by the POODLE attack in 2014. The protocol was reborn as TLS 1.0 in 1999 under the IETF and has continued to evolve through TLS 1.1, 1.2, and 1.3.
Why the Name Sticks
Despite SSL itself being obsolete, the name remains in common use. 'SSL certificate' is the everyday term for what is technically a TLS certificate. 'SSL VPN' refers to VPNs that use TLS for transport, regardless of whether the underlying SSL protocol is involved at all. This is roughly analogous to how people still 'dial' a phone with no rotary dial in sight — the term outlived the technology.
Practical Implications
When a website or VPN provider markets 'SSL encryption,' they almost certainly mean TLS — and you should expect a current TLS version (1.2 or, preferably, 1.3) for any modern, secure deployment. Genuine SSL is broken and should never be used. Any product that actually uses SSL 3.0 or earlier should be avoided.