TPACK refers to a way that we put technology into teaching. It stands for Technological Pedagogical And Content Knowledge. I really thought the best illustration was that the overlapping of Technology, Content and Pedagogy. TPK, or Technological Pedagogical Knowledge is just like TPACK, but does not encompass Content.
One really good example is TPACK would be like the video Ellie and I made for Newton's first law. It encompasses the teaching style, knowledge and the content of Newton's first law. TPK, however, is really just knowing how to use what is available to a teacher and making use of it. This could be just knowing how to make a really cool powerpoint.