Difference between "REPLY" and "REPLY ALL" in email

As many of us have known, there are "reply" and "reply all" in many email settings. What is the difference? "reply" means that we are reply to  and only to the person who had sent email to us. "reply all" means that everyone that is listed on the CC and BCC could see the email, although those recipients may not directly involve in the email. There is also a significant difference between CC and BCC. CC means that the CC recipient could see the email and it is known that the recipient could see the email. BCC means that BCC recipient could see the email but the other recipient would not know that BCC recipient.