An SSL certificate is a digital credential that permits visitors to a web site to verify the authenticity of the site and to communicate with it in a secure manner through the SSL (Secure Socket Layer) protocol.
These security certificates are granted by a duly authorised, independent agency, such as Thawte.
Your browser will inform you that you are on a secure server by showing a yellow padlock on some part of the screen. In the case of Firefox, the address bar will also be yellow. For greater security, you can check that the URL begins with https://www..., i.e., with an 's' after the last 'p'. If you click on the padlock shown in the browser, the information contained in the digital certificate authorising it as a secure server will appear.
The SSL protocol permits personal information and/or credit card information to be sent in a secure environment since the information is sent to the server in an encrypted format.