SSL is an acronym standing for Secure Socket Layer. In a nutshell, this is a technology which creates an encrypted connection between the server containing a website and the browser being used to view and interact with the website. This allows private information to be transmitted securely. The "S" portion of https in the address bar of a browser indicates that page is being protected by an SSL.
Websites now require an SSL Certificate. Most browsers will flag a site as "unsecure" if it does not have one. Monterey Bay Design offers free SSL Certificates with all our hosting packages. https://www.montereybaydesign.com/ssl