Had to hit the urban dictionary on that one.
This.
Gister:
One who gets the gist of a subject matter and knows enough to be dangerous with that subject in conversation or writing. One with proven gisting abilities. A gister can participate in conversations with subject experts without getting lost along the way.
If it's complicated and you don't have a lot of time, ask a gister to write it.
Not this:
Gister:
When one spends an unusually large portion of time with their sister to the point where they are mistaken as a couple. However, the word gister is used with a sexual connotation.
Right?
Right?!?!?!?
Yeah, I read it in a spy novel, don’t remember which one. The gister was the one who would take the voluminous intelligence reports and write the gist of it out for the President.