If you don't twitter then you're probably confused by what's meant by "Twitter @Replies". The term "@replies" referred to a way that people on Twitter have of replying to each other. Instead of hitting a typical "Reply" button to reply to someone you can type an @reply into the beginning of your text to reply to someone else's post.
An @reply is always directed to a specific person in reply to something they've posted. When someone replys to one of your posts using an @reply their reply will show up on your profile page, being that it's to you. Any post on Twitter can be replied to using @replys and @replys are always public.
If you don't want your message to be public and show up on your friend's Twitter profile page, then you wouldn't use @replys, you would use a direct message instead. Direct messages are private and can only be read by the person you're sending the message to.
Sending an @Reply or Direct Message
A typical @reply would look like this:
@username message
For example, if you sent this message: @linroeder How are you?
I would get a public message reading: How are you?
A typical direct message would look like this:
D+username+message
For example, if you sent this message: D linroeder How are you?
I would get a private message reading: How are you?
Tip: Always use your friend's user name, not their real name when sending them a message.
