Sticky Widget could be interpreted as something that would display the widget constantly. When you scroll the mouse up and down sticky widgets will follow.
Sticky widgets are used by widely and major websites are using the sticky widget like Facebook.
If you see any Facebook profile, right and left of the home page always follow even the mouse scroll top to down. Sticky widget is mostly used for displaying the latest information, new promotions and advertising etc. because through this way the visitors will always see them.