The Extensive Reading Foundation's bibliography now boasts over 530 articles with "Extensive Reading" in the title. About 35% of this rich and diverse body of papers were published in the past decade. A meta-review of this literature shows it is quite fragmented as evidenced by considerable variability in the conceptualization of extensive reading (ER) itself. For example, some researchers suggested that reading graded readers meant the subjects were therefore reading extensively (e.g., Kirchhoff, 2013; Yamashita, 2013) whereas others were more circumspect. Some suggested students were reading extensively by reading as few as 9 books or 140 pages over the duration of the study, or 5 books over an academic year (e.g., Robb & Kano, 2013; Shue, 2003), while others conducted ER over several years (e.g., Nishizawa, Yoshioka, & Fukuda, 2010), and yet others operationalized ER as the intensive reading of difficult material (e.g., Kweon & Kim, 2008). Given the variety and apparent fragmentation of the conceptualization of ER, we believe that it is necessary that our field share a common understanding of what ER is so we can evaluate and interpret ER research within a stable framework and talk a common language. But what is it that forms the core of ER? Is there a defining aspect of ER that determines whether a practice or research design can be called ER, or by its absence, not ER? This paper is an attempt to initiate a dialog to answer these and other questions.