You're referring to when web browsers draw a red line through the "https://" in their URL bars. It means that the browser does not trust the certificate that the site is using, for many possible reasons: it isn't signed by one of the root CA certificates that the browser implicitly trusts.

Why is https crossed out?

HTTPS, or Hypertext Transport Protocol Secure, is a variation on the basic protocol used to serve Web pages over the Internet. ... When you see "https" crossed out in your browser's address bar, you're not on a secure connection and should consider whether you need one for the website you're using.

Why is Google crossed out in red?

Google Chrome crosses out the "https" in the URL of a site if the site has a security problem. ... Regardless, if you see the "https" of a site's URL crossed out in red, you should avoid submitting any sensitive data to the page.