To get back to the main topic. Usually used when people get sidetracked a lot and need to understand that the topic is important.
The phrase comes from "Stargate Atlantis" a Sci-Fi channel production where a character, Doctor Rodney McKay, is asked to record a message in front of a camera to his superiors and loved ones. In the first scene he starts talking about "Leadership" and in the beginning of every other scene he gets sidetracked and talks about his girlfriends or his cats. In the end of every scene he says that he need to get back to the main topic he started with. "Back to Leadership."
Boss: So where are we at with that new product?
Employee: Well sir, it's ready and I got to tell you my wife and I tested it, and she just loved it!
Boss: Oh did she?
Employee: She even told all her friends about it and they are all excited.
Boss: I see... but let us get back to Leadership Jack!