What is autoscroll?

Answer 1

"Auto-scrolling is a feature that can be found in most mainstream modern applications. Pressing the middle mouse button transfers the application into the auto-scrolling mode. In this mode, moving the mouse down starts scrolling down the contents even when the mouse is no longer moving. The scroll speed depends on the distance between the current mouse location and the mouse press location. This works for all four directions (up, down, left, right)."

-http://www.pushing-pixels.org/?p=280