Google has found me a whole site on the subject. I've had little time to read the material yet but it looks quite fascinating.
Pity that most of the site consists of PDF files and I can't find a short one paragraph overview of what they are all about. I guess I am just going to have to do a lot of reading! The best definition I have found so far is about shifting from "teaching as telling" to "teaching for understanding".
Certainly in my school boy days at a traditional English boy's grammar school some 30+ years ago I was taught by 'telling'. Its amazing I ever learnt or should I say 'understood' anything .