A Twitter reply always begin with the "@" symbol, followed by the username. An @reply is a tweet posted in reply to another user's message which is usually done by clicking the "reply" button in their tweet. Replies are a way for users to talk with other Twitter users. A person can reply to anyone on Twitter, regardless of whether or not the user follow them or not. Conversely, anyone else can send a user a reply on Twitter regardless of whether or not the user follows them.