It’s a jQuery plugin that shows the latest tweets in a popup window. The popup box that appears can be dragged and resized. Clicking on the cross will make it disappear. The tweets are constantly being loaded in a predefined time span. This loading stops when the user hovers over the tooltip box.

If you want to configure and restyle the tooltip, you will need to have a look at the configurations of the Twitter Search Plugin. Many parameters can be set here, from style to timings.