CC: Full form of CC is Carbon Copy in Gmail. It means that the copy of the email is sent to any address that appear in this field.
It is included in the message header of the email. It is visible to all recipients of the message. If you ‘reply All’ to the email, everyone will receive the reply.
BCC: Full form of BCC is Blind Carbon Copy in Gmail. It means that the copy of the email is also sent to any address that appears in this field, but those email addresses do not appear in the message header.
All the addresses are invisible to all recipients. If you hit ‘reply all’ to the email, you will receive the reply only.