SSL stands for Secure Socket Layer (SSL). SSL is a security protocol that allows encrypted communication between a web server and an internet browser. It encrypts all data transmitted between the server and the user using an encryption key on the server. In layman’s terms, an SSL certificate ensures that the information being relayed between the web server and browser is only visible to the user and the website.
If your website doesn’t have an SSL certificate, a secure connection can’t be established. This means that the information transmitted is not connected to a cryptographic key. This impacts a customer’s/visitor’s confidence in your business and may even prevent them from ordering from you (if you are an eCommerce site).
To put it simply, the extra "s" means your connection to that website is secure and encrypted; any data you enter is safely shared with that website. The technology that powers that little "s" is called SSL, which stands for “Secure Sockets Layer.”
As a consumer, you always want to see https:// when visiting any site you trust with your essential information. As a marketer, you'll want to make sure you have an SSL or two for your audience.