Horizon Content Knowledge: Is It a Part of Content Knowledge or Contextual Factor?

Horizon content knowledge connects one teacher's present teaching with the broader subject matter knowledge. This notion has advanced the understanding of teacher knowledge recent years. To gain insights into the term, this paper reviews and discusses 24 academic articles related to horizon content knowledge. This review disagrees with locating the horizon content knowledge in the content knowledge. Instead, it argues that the notion of horizon content knowledge leads a new horizon to the context domain of Technological Pedagogical and Content Knowledge framework. Horizon content knowledge will have a deep influence on smart learning and learning system design.