What do the letters SSL mean on certain Web sites?

SSL stands for Secure Sockets Layers, a common way of securing Internet communications. SSL is used to encrypt data, authenticate the server and verify the integrity of messages. When data is transmitted using SSL, it enters a kind of tunnel that makes the information invisible to anyone other than the target for the data exchange. SSL is rapidly being superceded by https, which is now a safer way to shop and pay online.  (See also, How does Internet security work?)