SSL
In plain terms
The predecessor to TLS for encrypting web traffic.
Going deeper
SSL (Secure Sockets Layer) originally encrypted connections between browsers and servers; it's now deprecated in favor of TLS, though the name persists. People often say SSL meaning TLS.
Under the hood
All SSL versions are insecure and obsolete; modern 'SSL certificates' actually use TLS.
Examples
Legacy term for HTTPS, 'SSL certificates' (now TLS), deprecated protocol.
Think of it like...
Like an older lock design replaced by a stronger one, though people still call it by the old name.