HTTPS (HyperText Transfer Protocol Secure) is a protocol, or language, that allows communication between different systems. Most commonly, it’s used to transfer data from a web server to a browser to view web pages.
HTTPS is a secure connection. HTTP is not. With a standard HTTP connection, it is possible for unauthorized parties to observe the conversation between your device and the site you're visiting. HTTPS involves using a secure sockets layer (SSL) that helps create a secure encrypted connection between the server and the browser, thereby protecting potentially sensitive information from being stolen as it’s transferred between the server and the browser.
The SSL certificate encrypts the information that users supply to the site, which basically translates the data into a code. Even if someone steals the data being communicated between the sender and the recipient, they couldn’t understand it, thanks to the encryption.
Users expect a secure and private online experience when using a website; in penalizing HTTP connections, Google is taking steps to ensure they get it.
Back in 2014, Google recommended that sites switch to HTTPS. Until then, only sites with e-commerce pages really bothered to use HTTPS. As an incentive for switching over, Google announced it would provide HTTPS sites with a small rankings bump.
Now Google Chrome marks sites without HTTPS as non-secure if they collect sensitive information. Using HTTPS will increasingly be the norm rather than the exception.