Definition - What does @reply mean?
The Twitter @reply method is used when replying to a user via the format: @username message, where "username" is the recipient's Twitter handle. Another way to reply to a message is simply by clicking the tweet reply button. Message replies are received and saved under the Twitter @Connect tab.
The @reply feature is also known as a mention.
Techopedia explains @reply
Popular with Twitter users, the @reply feature is a convenient way to send messages to specific Twitter users.
An example is as follows: @chrisC0lumBus Congrats on your discovery.
Twitter messages sent as @replies are visible to the @reply message recipient's followers, or the general public, depending on the user's privacy settings. Private messages must be sent via Twitter's direct message (DM) function.