The short version of a long answer. When you don't want to give the long details for whatever reason.
When you just want the basic facts, not the War & Peace, x-tra long, version of the story, or someone's answer.
David:" Hey Jeff, How'd it go with Marcela this weekend?"
Jeff: "The short of the long....touchdown!"
Jeff:" Hey David, Do you have any beer left?"
David:" Well...I was gonna go to the liquor store, then Kim called me...and you know she has a nice..."
Jeff:" Dude....the short of the long..."
Daid:" Sorry, man."