HTTPS is the web protocol HTTP communicated securely. This is where SSL/TLS comes in. SSL is Secure Socket Layer and TLS is Transport Layer Security.
When handling sensitive content and forms, you should use HTTPS.
“Starting October 2017, Chrome (version 62) will show a “NOT SECURE” warning when users enter text in a form on an HTTP page, and for all HTTP pages in Incognito mode.”
– Google, August 2017