The language of email has its roots in office memorandums
When you select the contacts you are emailing you can place them in one of three fields:
To: - Put the email address here if it is for their attention and action
Cc: (Carbon Copy) - Put the email address(es) here if you are sending a copy for their information (and you want everyone to explicitly see this)
Bcc: (Blind Carbon Copy) - Put the email address here if you are sending them a Copy and you do not want the other recipients to see that you sent it to this contact
Tip: If you are sending an email to many people use Bcc (so you don't give away everyone's email address to everyone else)
Can't see the Bcc field?
Whilst you are composing your email click the Options Tab and then the Bcc button - it looks like this...