Smooth scrolling
Scrolling a pixel at a time instead of jumping a whole tile, so the world glides past evenly.
A character-cell display naturally scrolls a whole tile at a time, which looks jerky. Smooth scrolling needs a fine offset of a fraction of a tile, plus drawing one extra row or column of tiles just off-screen, ready to slide in as the coarse offset catches up. On hardware with a fine-scroll register it almost happens by itself; without one, the programmer has to stitch it together by hand.
When hardware scrolling was absent the trick had to be invented in software: John Carmack cracked it on the PC in 1990 with adaptive tile refresh for Commander Keen, redrawing only what had actually changed between frames. Smooth scrolling is taken for granted today, but behind it lie decades of tricks for avoiding a full-screen redraw every frame. Compare parallax scrolling, which layers depth on top.