The semicolon, ;, is the far look command. It is used to look at a square other than the one you are standing on. To look at the square where you are standing, press :. Far look does not allow you to see what is actually on that square, only what you think you see. This means you won't get information about undetected monsters (or traps), and if an item has been moved since you last had line of sight to the area, you can still use far look on that item's symbol. Because of this, far look generally gives more accurate information about something when you have direct line of sight.