What is the official meaning of the double space in a short story or novel?

I think it’s generally always a passage of time…I’m not sure there’s anything else it means. If not a passage of time, it might be a parallel storyline happening at the same time and the double space just divides the stories.

Are you talking about when a writer does something like this-
. . .
And then down here something completely new is happening. Some times it can be used to change the perspective, or switch to the POV of another character, but not really in a instantaneous sense. That would normally be done when the chapter changes.

Right. When a break stronger than a new paragraph but not as strong as a new chapter is required in fiction, authors will commonly use a bigger break. This is to indicate the passage of time, a scene change, an introduction of a new point of view, or some other shift in the narrative.

However, this extra line break has the disadvantage that it may be missed if it falls at the bottom of the page so sometimes you’ll see a type element or some other dingbat instead of the extra break. That also has the added advantage of being classy!