Timely Tweets, now easier to see. Starting today, Twitter are introducing a way to ensure that the most important Tweets from the organizations we follow reach us directly, by placing them at or near the top of our timeline. These Promoted Tweets will scroll through the timeline like any other Tweet, and like regular Tweets, they will appear in our timeline just once. Promoted Tweets can also be easily dismissed from our timeline with a single click.
source: Twitter Blog