A side-scrolling game is one you watch from the side, as if the world were a flat cut-through picture. The character usually runs left to right, and the background slides along so it feels as if you are travelling. Old Super Mario games are the picture most people have. It is a games word — you meet it in reviews, in shops, and among people who play — not in ordinary small talk. Games can also scroll up and down, or let you look from above; this word picks out the side-on, left-to-right kind. Though actually, many later games let you walk back the other way too; the name stuck from the early ones that only went forward.