Wikipedia remembers: "The Scroll Lock key was meant to lock all scrolling techniques, and is a vestige of the original IBM PC keyboard. In the original design, Scroll Lock was intended to modify the behavior of the arrow keys. When the Scroll Lock mode was on, the arrow keys would scroll the contents of a text window instead of moving the cursor. In this usage, Scroll Lock is a toggling lock key like Num Lock or Caps Lock, which have a state that persists after the key is released."
https://en.wikipedia.org/wiki/Scroll_lock#Window_scrolling