Teachers have always learnt from other teachers. They have always picked up tips from colleagues in their own schools (even if it has been unintentional, and the lesson was "what not to do"). And, over the last century, proactive teachers have gone further afield, arranging visits or swapping ideas with others in their subject associations or unions.
Thus, many teachers have long had what we might today call a personal learning network (PLN) - really just an group of people they have picked out who they think will give them ideas and inspiration (pages 4-7).
But the internet has made it infinitely easier to find and follow other teachers' work. The scale of sharing between teachers is now greater than it has ever been. What's more, the links being made are not just within a staffroom or a county - they are global.
Two years ago, I recall watching a primary-school teacher from Nottinghamshire wend his way through an international conference on education. Tom Barrett was repeatedly greeted as if he was an old friend by teachers from the US, Canada and Qatar. It turned out they all followed him on Twitter and were fascinated by his class's blog. They may have lived thousands of miles away, but Mr Barrett was part of their network.
However, you do not need to be a trailblazer or a successful teacher blogger to have a PLN. You do not even have to be online. Another part of the phenomenon can be found in the real world: the rise of Teachmeet events where teachers gather informally to give short presentations to each other. Instead of waiting for an Inset day or an expensive accredited course, keen teachers are freely sharing what they have found to work (that is why we regularly list selected Teachmeets on this page - see right).
This upbeat, grassroots movement stands in stark contrast with the political debate about how to professionalise teaching. These teachers are not waiting for a Government-approved master's degree - they are arranging their own learning. So, while the last thing the education world needs is yet another cryptic abbreviation, PLN is a more than worthy addition to the glossary.