To make contact; to cover all the possibilities. Comes from baseball where the runners need to touch the base to make a run legal. Mostly used by asshat supervisors who do no real work, but constantly engage in meta-communication.
Boss: "I'm just calling you to make sure we touch base."
Worker: "Alright, what do we need to discuss?"
Boss: "Well the first thing we need to do is touch base."
Worker: "So the point of this call is to have a call?"
Boss: "Exactly. That's why touching base is so important."
Worker: *muttered* "Go to hell, you recursive asshat."