Whenever you begin composing a new iMessage, your recipient can see that you're typing. That's because an ellipsis appears in their Messages app to let them know so. The purpose of this is to let people know that you're responding to them, that you haven't left them hanging. It makes the party on the other end of the message wait in expectation of your response.
While most people don't have a problem with this and actually enjoy the feature, some find it to be an intrusion of privacy. You could, obviously, just disable iMessage, and the issue would be settled. But that means the inconvenience of incurring possible SMS fees, and the inability to send messages via Wi-Fi, and on iOS devices which aren't iPhones.
As a response to this possible breach of privacy, a jailbreak developer has created a tweak to eliminate the 'now typing' ellipsis. The tweak is called TypingPrivacy, and it's available right now on Cydia's BigBoss repo.