The answer is GUTTERS.
A gutter is an inside margin, a blank space situated in facing pages of a book or adjacent columns of type or stamps in a sheet. In a graphic novel or a comic, gutters are around and between the panels (the individual frames that form the comic's story).
The gutter in facing pages: When we have a book open, the gutters are the spaces between one paper sheet and the other, we can locate it right in the middle.