SSL stands for Secure Sockets Layer.
It provides the means for submitting encrypted data to the web. It works based on a public-key/certificate system. The data is encrypted before it is sent over the Internet, then it is decrypted by the server once it has been trasmitted. If someone were to intercept a packet of information on it's way to the server, all they would see is a garbled mix of numbers, letters, and symbols.
