SSL VPN is a VPN that can be used with a web browser that uses an SSL certificate for the encryption. It has been replaced in recent times with Transport Layer Security (TLS), which is a more modern version of SSL. In the Security+ exam, the SSL VPN is normally used for legacy VPNs that don't support L2TP/IPSec.
Exam tip: SSL VPN is the only VPN to use an SSL certificate, and it only needs a web browser to make a connection. It could also be replaced by the more secure TLS certificate.