What is SSL?

The SSL (and TLS) protocol is the Web standard for encrypting communications between users and SSL (secure sockets layer) e-commerce sites. Data sent via an SSL connection is protected by encryption, a mechanism that prevents eavesdropping and tampering with any transmitted data. SSL provides businesses and consumers with the confidence that private data sent to a Web site, such as credit card numbers, are kept confidential. Web server certificates (also known as secure server certificates or SSL certificates) are required to initialize an SSL session.

Customers know when they have an SSL session with a website when their browser displays the little gold padlock and the address bar begins with a https rather than http. SSL certificates can be used on webservers for Internet security and mailservers such as imap, pop3 and smtp for mail collection / sending security

Courtesy of freessl.com