SSL is information technology in the form of a protocol. A protocol is a set of rules or procedures. SSL technology takes a message and runs it through a set of steps that "scrambles" the message. This is done so that the message cannot be read while it is being transferred. This "scrambling" is called Encryption. When the message is received by the intended recipient, SSL unscrambles the message, checks that it came from the correct sender (Authentication) and then verifies that it has not been tampered with (Message Integrity).
This is what allows us to send our credit card info over the internet without worrying about it being stolen. Just be sure that there is a closed lock or a complete key on the bottem line of your browser to ensure an SSL connection.