Not much.
SSL is short for Secure Sockets Layer, and is a protocol designed and implemented by Netscape. Version 3.0 of SSL was used as the basis for the Transport Layer Security (TLS) standard, version 1.0 (defined in RFC 2246, The TLS Protocol Version 1.0). The differences between SSL 3.0 and TLS 1.0 are not substantial, but the two protocols do not interoperate. TLS does, however, support a mechanism to back down to SSL 3.0.
edtFTPj/PRO supports TLS 1.0. 1.1, 1.2 and 1.3. SSL 3.0 is obsolete.
We generally use the term "SSL" interchangeably with "TLS", as SSL is more commonly known.
