"Flexible SSL encrypts traffic from Cloudflare to end users of your website, but not from Cloudflare to your origin server. This is the easiest way to enable HTTPS because it doesn’t require installing an SSL certificate on your origin. While not as secure as the other options, Flexible SSL does protect your visitors from a large class of threats including public WiFi snooping and ad injection over HTTP." - More info at https://www.cloudflare.com/en/ssl/.