The status line is composed of two areas: on the left a status bar and on the right a progress bar (displayed only when background tasks are running).
The progress bar is used to display information about on going operations such as builds, searches, or VCS commands. These tasks operate in the background, and can be paused/resumed by double clicking on the progress bar: this will open The Task Manager. In addition, you can click on the close icon on the left of the progress bar to interrupt the running task.