SSL stands for Secure Socket Layer. It is a protocol for allowing encryption between the browser and the web server you are accessing. This protocol encrypts the data to ensure that it cannot be spied on in transmission, which means when you’re accessing data from the server, it is returning it to the web page for you to see.
An SSL certificate is used to verify the identity of the server or website you are on. That certificate is used to decode the data coming from the server to ensure that the key in the certificate can match the key used to encrypt the data from the server. If you visit any website and see a padlock in the information bar, there is a certificate, and the connection is secure.
SSL has progressed to TSL (Transfer Support Layer), an enhanced version offering more benefits.