A slider, also known as track bar in Microsoft literature, is an object in a Graphical User Interface (GUI) with which a user may set a value by moving an indicator, usually in a horizontal fashion. In some cases the user may also click on a point on the slider to change the setting. It is different from a scrollbar in that it is typically used to adjust a value without changing the format of the display or the other information on the screen.
Usage with progress bars
Sliders are also combined with progress bars in the playback of streaming media over a network connection (e.g., YouTube videos) in order to show the content buffering position versus the playback position. This is done by superimposing a colored shaded area (progress bar) on top of the slider, indicating whether the user can "jump" forward or not.