Flexible,Full,Full(Strict)の３パターンあるね ここの説明が一番わかりやすい https://support.cloudflare.com/hc/en-us/articles/200170416-What-do-the-SSL-options-mean-
support.cloudflare.comWhat do the SSL options mean?A short version of the answer to this question is: Only choose “Flexible” if your origin webserver cannot accept secure (HTTPS) connections. Choose “Full” if you have a self-signed SSL certificate,...