An inbox is a screen on which you may read, organize, and reply to messages that have been sent to you. Inboxes in email clients are a popular example. Social messaging systems also use inboxes. Facebook and Twitter, for example, both use an Inbox to keep track of newly arrived messages and allow users to manage their messages. An example would be in WordPress, where the reader has an inbox from which it can read comments from other readers or reply to those comments.