The notion of reflection nowadays is considered crucial in the field of teaching and teacher education. However, although the great majority of approaches to reflection are grounded on the same main theoretical sources, the meaning of this notion is unanimously recognized in the field to be ambiguous. This article aims to look for clarity about what reflection is, what it is not, and how it works, by closely revisiting the seminal works of Dewey, Schön, and Wertheimer. It is argued that reflection is a descriptive notion--not a prescriptive one--and that it refers to the thinking process engaged in giving coherence to an initially unclear situation. The article then identifies some aspects of how reflection works, and some current widespread assumptions about reflection, which are insufficiently warranted, either theoretically in the writings of Dewey or Schön or empirically in the observations of reflection processes.