What is a TLS certificate?

A TLS certificate is the certificate a server presents during a TLS handshake so the client can verify its identity and agree on encryption keys. It is exactly the same file most people call an SSL certificate. The rename comes from the protocol, not the certificate: SSL was the original protocol, TLS replaced it, and the certificate format carried over unchanged.

The reason both names survive is timing. SSL reached version 3.0 and then was superseded by TLS 1.0 in 1999, but by then "SSL certificate" was the term everyone used, so it stuck. Today SSL itself is fully deprecated and disabled in every current client; the connections are all TLS, most commonly TLS 1.2 and TLS 1.3. The certificate you buy or generate is described either way by different vendors, and it is the same X.509 file.

What the certificate does in a TLS handshake is precise. The server sends it early in the exchange. The client walks its chain to a trusted root, checks the validity dates, and checks the hostname against the certificate’s name list. Only then does the client trust the server’s public key and finish setting up the encrypted session. A problem at any of those checks stops the handshake with a certificate warning.

So when a tool, a certificate authority, or a hosting panel says "TLS certificate" where you expected "SSL certificate", nothing has changed about what you need to do. Serve it with its chain, keep it inside its validity window, and cover every hostname you answer on. The only place the SSL-versus-TLS distinction still bites is in configuration language, where an option named for SSL, such as an ssl_certificate directive, is really configuring TLS underneath.