SSL, Secure Sockets Layer (and its successor Transport Layer Security) is a Net-based security protocol that ensures communications between computers is safe and unhackable--essentially so that no one can "listen in." It works like this: A server and computer connect together and say hello, digitally. This bit is unsecured. The two machines exchange a "key" which unlocks a private line that only they can communicate on.
These private exchanges are the basis of safe e-shopping, including credit card transactions. On the server side the site's owners can be certain they're speaking to a genuine customer, who's data can be trusted (to an extent).
