Hotkey question

Can anyone tell me what hotkey it is that ... idk what to describe it as, but if you are in a maximized client, the edges go Red, and your mouse cursor no longer interacts with the sides. This allows you to freely move your mouse to your other monitor in order to client a window with out Alt+Tab and give focus to that oh so important Chrome window... but it also prevents you from moving your window around like normal (for me anyway) which made me absolutely useless because to move my screen around the map, i was 100% forced to use the minimap... which is not great imo for late game team fights.

I reviewed every hotkey in the new client, and nothing I tried worked... Also nothing seemed relevant.