SSL or Secure Socket Layer is the standard for encrypted communication between web browsers and web servers. It ensures that the communication between the browser and the server is private and encrypted.
SSL is an industry standard. To protect the online transactions with their customers, millions of companies used SSL encryption technology in their websites. It allows sensitive information such as login credentials, social security numbers and credit card numbers to be transmitted securely via the internet.
Google also prefers SSL certified websites when compiling SERP. The URL prefix changes from http:// to https:// and a padlock icon is visible in the address bar, when a website is secured via SSL.