A term coined by NBC's 30 Rock. It's when you shake your index finger at someone to make a point to whatever you're saying. First used in a season 5 episode called "Plan B" by Jack Donaghy (Alec Baldwin's character).
Liz - "You're looking out for us, right? Pounding on desks and doing whatever this called." (she's shaking her index finger)
Jack - "Power wagging."