In the example [shown right], the gutter is the white bar space between the larger upper portion of the splash page and the smaller rectangular panel at the bottom. This lesser image effectively manages to complete the story action on the opening page of this comic book tale and also "invites" the reader to turn to the next page to find out what happens next.
These days gutters are few and far between, but for decades they were a vibrant, necessary & important part of graphic storytelling. Modern conceits have allowed the majority of working comic book artists to adopt the full page bleed where the art is allowed to run to the edge of each page, rather than having a white border around it. In the past, bleeds were occasionally used to create the illusion of space or to emphasize action, but they were hardly the norm for most of comics history - - - as they are now.
In my opinion, the rampant use of full page bleeds, allows mediocre artists to cheat.