The most recent Infinite Thinking Machine episode takes a crack at defining and explaining different modes of blended learning. In short, "you mix online learning with face-to-face instruction on a regular basis." The model -- and products -- teachers choose to use will depend on their instructional styles: teaching content or more open-ended styles, like project-based learning.
This episode brings up some important points: cost efficiencies, "magic bullet" solutions, and content delivery should not be the goal for using blended learning tactics. Rather, the focus should be on allowing kids to be creators of work that's relevant to their own world -- that's what will catapult "blended learning" out of the next edu-fad and qualify it as a true change agent.