Split-screen scrolling
Holding part of the screen still — usually a status bar — while the rest scrolls, by reloading the scroll register partway down the frame.
A whole screen otherwise scrolls as one piece. To pin a fixed HUD at the top or a map at the bottom you had to fool the hardware: wait until the beam reached the seam, write a new value to the scroll register, and let the rest of the picture draw with a different offset. The timing came from a sprite 0 hit or, later, the mapper's scanline interrupt. The C64 and Amiga did the same with raster interrupts and the Copper. Vertical splits were harder than horizontal ones because the register had to be hit on the exact pixel. Almost every platformer with a score bar leaned on the trick.