Closure explains what happens in between the panels. The audience comes up with their own interpretation of the gap between panels, and this interpretation can be different for each audience member. It can also be used for the reader to interpret what the ending of the comic means by the use of the panels.
In hypertext and networked thinking, closure happens between linked notes—readers construct meaning by traversing connections, each creating their own understanding from the same garden structure.
Understanding Comics by Scott McCloud