Phrase popularized by the 2nd series finale of the BBC programme Sherlock--put simply, not one's responsibility, strong suit, or "area." Can also be used in terms of personal preferences--e.g. "blue jeans really aren't my division," or in reverse to show an interest in something--e.g. "Tom Baxter's face is my division."
Mom: please put the laundry in the dryer.
Me: Not our division. (You can say "not my division," but definition wouldn't let me.)
Friend 1: College is so not my division.
Me: mmmm dinner and a movie, looks like my division.
Me: Not our division. (You can say "not my division," but definition wouldn't let me.)
Friend 1: College is so not my division.
Me: mmmm dinner and a movie, looks like my division.
by anonymous221B March 20, 2012