SSL is short for secure socket layer - a technology that encrypts communication between users and a website. This encryption ensures that important data such as usernames, passwords, and credit card information is sent from the user to the site without the risk of interception.
An SSL certificate is a certified piece of code on a website that binds this encryption to the organization responsible for the website.
An SSL-certified website runs on https protocol. This activates the browser padlock or a prominent green browser bar to show visitors it is safe to browse. Reputable websites use SSL to protect their customer’s data and their online transactions; their reputation depends on it.