Blended Learning generally refers to the combination of classroom with electronic learning. A typical example would be a classroom training that places various pre-work, homework, tests, and follow-on sustainment activities on the Web. The idea, a good one, is that the trainer can "offload" what is more efficiently carried out at a computer screen rather than in a classroom. A proper "blend" maximizes both media (classroom and computer) for what they are best suited.
In A.D. 750, the Arabs, importing and improving a technology from China, created "paper-enabled" learning (as we might call it today). By substituting inexpensive paper for expensive animal-skin vellum and parchment, the Arabs created the paper-based manuscript, a mass-media platform that—combined with the oral tradition of ancient Greek learning—helped ignite an explosion of learning that would lead to the Arab renaissance (800–1100) as well as to the subsequent Italian Renaissance (1400–1600).
Blended learning can also refer to the combination of videotaped lectures or live Webcasts with online tests, or of personal coaching sessions with a Web course. There are endless variations. The key concept is to leverage each medium for what it does best in order to deliver the biggest payback in ROI.
It should be added that world-class learning has always been "blended" learning. The very first classrooms of ancient Greece were "blended" learning combinations of traditional Socratic classroom discussion (oral medium) with the new hi-tech medium of the scroll (print medium).