Screen Size?

Hello, my students and I are crash learning arcade. I have a question regarding screen size. The doc mentions 160x120

In the Cherry Pickr Tutorial, the user can move beyond the cherries that are placed in random locations bound by 160 and 120. I have hunted around to find an explainer on screen size, but none of them are answering my question. Is there some other measure in play here? How is the boundaries of the ‘room’ set?

Setting a tilemap will define the boundaries of the map. Any location outside of the map is marked as a wall so the player can’t move outside. Your tilemap is 16x16 tiles and every tile is 16x16 pixels so the map is 256x256 pixels!