@reply

You send an @reply (at reply) to a single person, but an @reply is not a private message. @Replies show up:
*In your timeline.
*In the recipient’s timeline (only if the recipient follows you).
*In the recipient’s @Username mentions list.
*In the public timeline.
*In the timeline of every person who follows both you and @reply person*.
*This is the default setting. You can change your @replies option under Notices in your settings.




Twitter displays every tweet that contains your @username in your @Username mentions list along the right menu options.



Reply to a Tweet
If you read a tweet and want to reply, simply hover your mouse over the tweet until a back arrow appears on the right. Click the back arrow and Twitter starts creating your @reply. Twitter provides a link back to the original tweet so the @reply recipient can link the reply to the tweet. Using @Reply To Start a Conversation




You can send an @reply directly to a person without replying to a tweet. Type @ + the username and your tweet. For example: @WorkingGirl Great news about your book launch party!