(Example: §, ½ or | on Nordic (Danish, Finnish, Norwegian, Swedish) keyboards, circumflex ( ^) on German keyboards, ² on French keyboards, \ or | on Italian keyboards, ` on Brazilian keyboards, ' on Turkish keyboards).
The key is the top left key under escape, on non-U.S. Other keyboards with different layouts will differ, but the key is usually to the left of 1 or just under the Escape key ( Esc). keyboards, and the not symbol ( ¬') on UK keyboards.
Use the backquote key ( `) while in-game (Unpaused).